I have a similar rule despite the odd individual attempting to be a good Samaritan, standing orders are to refuse. Everything we do is open to scrutiny. When setting up the firing ranges we were told we had to be careful and generic since attack profiles are considered sensitive. We were not given specifics and for game purposes that's ideal as players have a broad ability you need to set comfortable margins. Sometimes you get amazing data from Boeing, I have on my desk right now as it happens a full colour glossy sales brochure (circa 96? I found it with some old newsletters dated then) for the Longbow with a nice insert of the weapons page (in mono).
Guidance on the FCR was a bit thin as you can imagine but it got better, partly thanks to the blog and the feedback loop it creates. You only have to post a picture of the wrong gun here at SimHQ and you get a ton of helpful people telling you how wrong you are
it's pretty fantastic.
Janes was a great reference since they included a sales video of the desktop simulator showing the FCR in use, the bi-directional sweep etc. I copied that behaviour (I'm told it's still not quite right but it matches how it mostly worked in LB2). For Apache-Havoc I offering some guidance here and there, some of it was wrong; the hover position box for example. If you didn't know I was responsible for some of the technical writing and history in the Enemy Engaged manuals, that paid for a laptop as I recall plus I got to keep and store about 20lbs of research material collected from brochures and publications. Being a perfectionist I strive to make it look authentic as opposed to realistic, only those who really know can tell the difference and they are not saying much except "pretty close". YouTube offers a wealth of data, often they scrub out naughty bits but subtle things like the LED matrix in a video of the KBU being used to send an "I love you" message gave us a font and colour. Can't remember if there was a cursor but I added one anyway. More animation looks cool.
Some of my own photos of the aircraft are used in game, I recall Matt Wagner sending my some renders of their A model with missing parts identified asking if I could help but they were pretty obscure areas (which I've since got good data on but it was a long time ago). Now we're collecting CH-47 material like crazy (had one enquiry from a movie set as Daves renders were spot on).
Oh, as a funny aside one military contractor (I won't name names) asked for advice on fonts for their own simulator gauges. What was funny is that I had to explain that in Combat-Helo ALL of the vector graphics and characters were HAND CRAFTED by me on pages torn out from my lads school math books and therefore difficult to export. All vector co-ordinates, no bitmaps. So yes, we do old school development
Still have those sheets.
Perhaps the best single most important reference was the cockpit layout thanks to the British MoD who put 360 quicktime cameras in both seats on their website. So if our cockpit looks a little different to US ones it's partly that. Also we have the EECH style UFD and MFD bezels and button arrangements. This is party a style choice, a functionality choice and also a nod to the work that a certain old friend who helped build a render-horse cockpit back in 2002 (the same one used in the Outerra demo). But that's another story.
There's a LOT of love and work in our aircraft, teasing it out of nothing has been pretty much the bulk of it. Stories behind a lot of it.
You need to remember that DCS is a series that strives to make accurate simulations, we're in it to make a game, three guys making old school combat sims with a bit of depth (you'll see me repeating the words authentic instead of realistic). I do have an educational motive however and if you ever get me drunk enough I'll tell you what it is (I don't drink much so it wouldn't be too hard).
On reflection I think it would have been more fun making casual iPhone games. I quite enjoyed that. Not that I don't enjoy this, but it's certainly gone on a bit.