From what i've seen:
LC: Only produced in the old-fashioned auto-inject case
LCII: Mostly used the old auto-inject case, but some later LCIIs used the newer LC475 manual-inject style case
LCIII: Most LCIIIs i've seen used the old-fashioned auto-inject case, however my October 1993 Singapore-built LCIII (which is definately a standard LCIII, not an LCIII+, we got this machine when it was brand new, i am the original owner and know its entire history, and can confirm it is still on its original mobo) has the newer manual-inject style case
LC475: By this time they had mostly switched over to the newer manual-inject style case, however some very early production model LC475's used auto-inject cases, from what i've seen.
For the record, my LCII is an auto-inject one, and my LCIII and LC475 are both manual-inject.
Anyway, i'm thinking that they must've switched to manual-inject half-way through 1993...they must have just used up whatever auto-inject cases they had left on whatever machines and then switched over to the manual-inject cases once supplies of the older cases ran out.
Also, another thing to note - all auto-inject LC cases have the model name silkscreened directly onto the case, and all manual-inject LC cases have "Macintosh" silkscreened onto the case, and the model name silkscreened onto a tag which was glued onto the case.
"Bite off more than you can chew and then chew like all Hell" - Peter Brock