I did as you suggested, made the containment research depend on the several alien autopsies, and made each autopsy unlock it.
However, now when I research the first corpse (which yields an autopsy), I no longer get the "We can now research Alien Containment" message... but the research is available once I go back to the Lab interface.
Apologies for a super late reply, but I had taken (am taking) some time off as I'm occupied with other matters at the moment. I saw your message the other day but didn't quite have the leisure to provide any input until now
Anyway, I have come across the same quandary. For some odd reason, corpse-dependent research topics will trigger the "we can now research" message for any and all corpses (except the one that triggered the unlocking) that are listed under said research topic's dependencies
after said research topic is researched,
as long as those corpses are in your base's storage.
So if you have every alien corpse listed under Alien Containment's dependencies and you have Muton, Sectoid and Ethereal corpses in your storage, then after researching Muton Corpse (to pick one), unlocking the Alien Containment topic, and
then researching Alien Containment,
this will trigger the "we can now research" message for Sectoid and Ethereal corpses.
The problem with having autopsies do the unlocking is, as you noticed, that autopsies do not trigger the "we can now research" message, even though the research topic is still unlocked at the lab.
A fix for this should be requested here:
https://openxcom.org/bugs/openxcom (I'll try to make a request later since I'm incredibly busy, otherwise feel free!)
Either:
(a) corpses should be "unlinked" from being erroneously triggered for research by the research topic under which they are listed as dependencies, or
(b) autopsies should correctly trigger the "we can now research" message for whatever research topic they are unlocking.