Games recognising external floppy drives
 

Why is it that with some titles, you can put supplementary disks (i.e. disks other that disk #1 of however many disks make up the game) into external drives and they load fine from the prompt to swap disks, but with others, they'll only be accepted in df0: ?

Some times games will specify "any drive", others expressly specify "df0:" and others leave you to guess what might work!

Lazy programming?

Adding drives takes RAM.

Maybe some of these games are already pushing the 512K Chip RAM so...

the fact that there were not many external drives at the time could be another reason;
most of the userbase was splitted between default A500 or A500 1MB;
but yes, a bit of shame later in time, when games were mostly multidisk

sometime also, some cracks broken that feature, compared to the originals
and sometime the opposite too iirc, with some crack fix to enable it