It sounds like the newer cases you are talking about are either the Just Toys case (which features the lower costume detail
and slightly different head), or possibly even one of the Disney clear back cases.
The most significant change to the vintage cases was the transition from the two to four hinge design, which was pointed out
above. (otherwise, there are no differences). The latest documented MIP example that I've been able to find is still on the
ESB 41b. (to date, the only exceptions to this are still the Canadian 32b and the LL. These both have 4 hinges)
That's pretty much it from a structural standpoint. Anything that doesn't look like your standard, vintage case, it just one of two
newer cases I mentioned previously. If you wanted a production/MIB break down, I can give a better listing of what I currently
have.
Here is the JustToys case for reference:
(costume details added, and head/shoulder proportions are changed)
Bill