If extension is 'rom' or 'bin' then it may or may not have the right header.

Similarly, if an ATR extension should run since those are floppy disk images and don't have any header issue. Usually if you see an extension with '.car' then the header should be intact should likely run fine. Unfortunately, there is a mish mash of images floating around and hard to tell. Some emulators have a built in database that use a checksum to determine how to launch cart, but that isn't always foolproof (i.e., won't run). There also can be some challenges with cartridge based Atari 800 games in that the some sources didn't have the proper headers to tell the emulator what type of cartridge was being used. The path to those is determined by the file .atari800.cfg which is usually in your root Retroarch directory. If you have some games launching, then likely not the issue. My reference to Atari roms was that you have the appropriate machine bios roms required.