It's OK, but MESS support lynx headerless roms if extension is '.lyx'. (If you rename a no-intro rom from '.lnx' to '.lyx' works fine).
You can see the code here
I'm the one who wrote that code, so I'm fully aware of what MAME loading routine supports. But as you can read in the comment to the code, that code which loads games based on their size is just an heuristics which might fail for carts which use different PCBs (Lynx dumps are in a pityful state concerning documentation of the actual cart content, so we don't even know what cart uses what PCB, with the result that games might fail at a very later stage when an unemulated bankswitch is required... unlikely, since Huygens tested most games extensively, but still possible)
the correct fix is to change extension to the files, or to explain no-intro guys that their creating unsupportable sets by removing the header with no advice to the users.
I think that's being excessively strict. There are under 50 total Lynx commercial ROMs, so it would be quite easy to test if a given fullpath loader is detecting properly.
tentative fullpath loading is already supported if the user changes the extension to .lyx
maybe no-intro should change extension to their dumps, but extending the heuristics to the format .lnx, which was created to use the header information, is not really a solution IMHO