Here, I will explain what I know about the CampgnXX.DAT files. These files contain quite a bit of information,but I will go through the most important segments.
First relevant info is the Aerodrome number. It is highlighted in cyan with purple border
Next, we have promotions. The dates in the campaign files are "coded" by days, however, but I will give you a few references to go by.
10EF 2400 is 1915 Jan 1
7FF0 2400 is 1916 Jan 1
EDF1 2400 is 1917 Jan 1

Anyway, it is easier to show by example. Here is a screenshot from the German campaign file available below, starting Jan 1 1916:

The first highlight in light blue is which aerodrome the pilot is currently at and then in plain text the squadron (Here Jasta 10). The 00s in campgn00.dat have to be changed BY YOU to fit into the sequence of pilots in your campaign folder.They are highlighted by a light blue circle.
Next part of interest is in yellow squares with red borders. The first is the ranks held, 01=Feldwebel and 00=Unteroffizier. The next segment in the same colours is the dates of these promotions. This is the more tricky part.
Then we go past the Snipp, which is only a sequence of FFFF and 0000 and the odd BBFA.This is where paint schemes for Your plane or squadron are located.
Here we find a strange date: 6BF2 2400 which is April   1917. I have no idea yet what it is used for.
Next is a VERY important bit of info in a grey box with double black border. This is the current date. 7FF0 2400=Jan 1 1916. This is the variable you change to move your campaign backward or forward in time. Selecting anything before August 1915 is futile, since all the early squadrons start on Aug 1 1915. There is nothing in RB2 before that. ("And the Earth was without form and void...")
The grey box with dark blue border is the pilot nationality. As usual, 0=german, 1=french, 2=british and 3=US
The light blue box with blue border is the 5 pilot traits: 961  89869  99310  57771 and 75108.
In grey we have surname and given name.
The red box contains enlistment date. This is normally follwoed by the picture bitmap file, but I didn't put one in.
The reason for the "July, August Sep" is a total enigma and their presence seems extremely redundant.
The last bits of info is Squadron ID in grey, current rank (just one byte!), # victories and # medals, followed by 0D0F 0B3F and a whole bunch of 0000.
The following is courtesy Tymophil:
The blue box with the yellow field is player score divided by 100. (For those who are mathematically challenged: Multiply this number by 100 to get Pilot score). The Bark green box with pale green field is Pilot Status:

00 Active German Pilot
01 Active Allied Pilot
05 Maimed
06 Killed
07 Maimed (again)
08 Prisoner of war
09 Imprisoned
0A Executed

Finally, the red box with pale blue field is the region of operations:

00 Marne
01 Flanders
02 Verdun
03 Alsace

Click on the following button to download this pilot. He has to be renamed as CampgnGE.DAT does not work. Just replace the GE with the next Campaign number in the Campaign folder. Don't forget the "00" at offset 0x3E, the AerodromeID and Squadron name.

This was what a newly started campaign file looked like.

Now,  I will delve into what an ongoing campaign file adds to this. The following screen shot is from the same campaign after clicking Done but before going on the first mission. Squadron mates have now been added, as well as local squadrons.
First off, we notice that the information in the yellow box with red border has changed. Another really strange thing we notice is that Early German Pilot's 5 pilot traits have changed. The first has dropped and the other 4 increased to maximum.

I have no idea what the garble in grey starting at D32 is... Any ideas? Anyone?
The light purple box with yellow background is the number of Pilot records in this file. In this case it is 8 (9 minus you = 8). When Aces are KIA, this number increses to include them as well. This is where you can increase your own squadron from 9 to 12. It's a LOT of work...
Going to Hauptman Achmann. He is listed as number 41. This number increments for every new pilot joining the squadron. Why 41? Because the Aces end at 3F, that's why. We find that he signed up for service Feb 8 1915 (pink box) and has the picture of gerace02.bmp. That last was easy stuff. Blank info, followed by SqdnID 1000 0000 and his rank 04 (red box). Then we have some numbers (B160 9243) in the light blue box that I believe are flying time. This might bear on transfers later (?). Anyway, Achmann has flown ... 290.75 hours! wow!
Next, in the grey box, we find 01000000, which is the number of kills Achmann has been credited with (one). We now find plain dates (why the mix?) Dec 27 1915: Morane Bullet. (actually my campaign pilot's squadron has shot down about a third of all the Morane Saulnier Type "N" deployed by this date, LOL (remember that there were only around 40 of them deployed by the French?))
Unfortunately, Achmann has received no awards yet ( grey box with grey border) for this super-human feat! We'll check this farther down on this page, when I go through the campaign file after the first mission.

The D00F0B3F is possibly Float and would translate to 0.54321003. It is present in ALL pilot segments - even the Player Pilot. What it is? Don't know yet.

#42, Mr Weiss joined Fliegerkorps Oct 8 1915 and is an Oberleutnant. He has a staggering 109.76 flying hours (as a comparison, my "real" campaign pilot joined the service Oct 1 1916 and now, 125 kills later in late April of 1917 has flown a more reasonable 54 hours), and 2 kills: Dec 14 1915 he shot down an allied balloon and Dec 28 1915 a, you guessed it: MS Bullet.

And here it is! After the first mission, there are many changes:

Underlined in pink is the current date. Jan 5 1916.

The first light blue box contains player flying time in Float format. Pilot Stats gives me 0.6 hours and converting 3F122222 to Float gives me 0.57083333. Close enough. So this is FLYING TIME.

The next two segments are # kills and # medals. None as yet.

After the first [Snipp] we find Achmann again. During the first mission he shot down an allied balloon. At offset 509C we find that # kills has increased to 2 (red circle) and the second kill has been added in the grey field. In the grey box, we find that he got a medal too. EKII.
Even though it is not evident in this shot, there is an indicator at 50F0, just before the next pilot. If it is 6, he's dead. If it is 1, he's assigned to a mission.

After the last "Snipp", we have the info for the latest pilot to join the Jasta, Reichlinn.
Now, we have the Local Squadrons data.
First, at 56F4 in red, is 0E00 0000. This is the number of active squadrons in the region.
The first squadron is 8400 0000, in the light blue box. A quick peek at our list and we find that this is 1 Sqdn, RFC.
It is followed by unknown data, and then, in pink, we have squadron quality. 3=Good. F000 0000 in green, is the current aerodrome, Bailleul i Flanders.
Following is 2 sets of 0C00 0000, which is the number of planes in the squadron. there are acually 3 instances of this, but I am not quite clear as to the reason for this. Then we have a mysterious 0000 0000. Now, we revisit the hint from the "How-to" page. The pink box contains: # of different A/C used=1; 13=Morane Saulnier type "N"; and then we have the 0C00 0000 again. I guess it is a reference to the following list of every single aircraft in the squadron. They are obviously all MS "N"s, and each plane has been underlined alternately in green and red for clarity. If there have been casualties, there would be a 8020 0500 before the plane, and an ordered plane has 4021 0500 in the same spot. Allocated planes for missions have a 0100 0000 preceeding the A/C in question.
In the next light blue box, we have the next squadron. 9D is 12 Squadron (Bomber/Recon) with BE2s.

[Under construction...] 1998 05 29