Interesting. That makes sense I guess. Kind of good to know. Is this known to apply to any games other than UFO and Ten Desires? It's much harder to test on other games where you can't max out on resources in stage three, but if it's a holdover from Subterranean Animism it probably doesn't.
The PCB+ main-series games are easy enough to test using stage practice. I've tested most of them anyway, might as well list what happens:
- HRtP: if you have 6 lives, nothing happens
- SoEW: if you have 5 lives, score extends give you a bomb instead (not sure what happens if you collect a 1up item while at 5 lives, but that would only be possible by reaching 5 lives via score while a 1up item is already on screen, since otherwise the enemy will drop a bomb item)
- PoDD: only gives 2 extends
- LLS: no life limit (the game gives 8 extends, so 10 is the maximum reachable without increasing the starting lives, or 13 with increasing it)
- MS: no life limit (actually, from cheat-assisted testing, it seems 1up items have no effect if you have at least 98 lives [stored as 99 in the game's memory], but point item extends still work)
- PCB: if you have 8 lives, you gain a bomb instead
- IN: if you have 8 lives, you gain a bomb instead
- MoF: if you have 9 lives, extra lives have no effect, not even a sound effect (note, you can only reach 8 in the main game, but in stage practice you start with 9 lives like in SA; it's possible a 7th extend existed in development but was removed due to how many bombs are available)
- SA: if you have 9 lives, new life parts have no effect
- UFO: already mentioned
- GFW: motivation stops at 1000% (and dying there reduces it to 900%, as expected)
- TD: already mentioned, also the game only gives 6 extends so the glitch can only occur in stage practice. Interestingly, TD actually has 10 extends programmed in (8, 10, 12, 15, 18, 20, 25, 30, 35, 40), but it's impossible to reach anything beyond the 6th without cheating to set your life count or pink spirit count or something (there simply aren't enough pink spirits to reach beyond 13/25 even if you could trance every one of them).
I haven't tested PoFV, or EoSD (need to set the starting lives higher, otherwise there aren't enough extends to gain a life when you already have 8).
As for extra bombs, PCB/IN do nothing if you already have 8 bombs, HRtP gives you 10,000 points, SoEW gives you 65,530 points (times the difficulty multiplier), GFW stops at 300%, LLS doesn't seem to cap, and it isn't relevant in the other games besides UFO/TD (due to different bomb systems, or in the case of MS/EoSD there aren't enough extra bombs to reach any limit that may exist).