Yeah, basically what you said there. I'll scour through as many photos as I can locate throughout the year. Then, anything remaining that I may still not be certain about I'll usually switch to video from the year and search for any decal sheets from the year. This will often times reveal everything. But, in some cases none of the above ends up really identifying certain logos. At that point I'll usually contact modeling groups, photographers from the era, etc.
Once I have what I need I typically draw everything in Illustrator, Photoshop, or a combination of both. The more common stuff I can often just pull from 'Brands of the World' and turn them into conting decals, which is nice. But, a lot of the cars will have a couple obscure things so I'm constantly having to draw up new logos. That Ricky Rudd car I had to draw fresh logos for just so I could get everything sized right. I drew a new hood Tide logo from scratch, the numbers, The Tide's on the quarters, a couple quarter contigs, and the Tide/slogan on the tail.
It's fun to bring them to life, but I will say I don't really enjoy the research when it hits roadblocks. But, I'd say 97% of the time I'm able to acquire everything needed for accuracy on at least one car from the season. Sometimes I'll think I'll have to skip a logo and then a few cars later there's another car with the same one and it's entirely visible, solving the issue on the previous car. That always rules. lol
thracingphotos.smugmug.com
