Update: FE7 event id 0x91, if set, makes it so things like the boss icons, status effects, etc don't show on the map. Write 05 E0 to 25BC6 to skip this (I'm assuming it's a leftover debugging thing).
0x00-0x27 - Temporary IDs, work exactly as intended (0x0 is always 0, 0x1-0x7 are reserved, I think)
0x28-0x3F - Temporary IDs that also work, but don't get reset when beginning a new chapter unless you suspend and resume.
0x40-0x63 - Should be temporary, but there's data here they would go. Don't use these.
0x64 - Got kicked out of both Temporary Club and Permanent Club. Sorry, kid.
0x65-0xA4 - Permanent IDs, work exactly as intended (0x65 is Game Over, 0x91 is reserved for above, and some others might be reserved?)
0xA5-0xFF - Should be permanent, but actually start overwriting the temporary ones, so don't use these.