Hi, MrC. I'm not sure I understand your questions, but I'll answer the parts that I do understand so far.
I am not aware of any transition in the UUID style, but it is not impossible. What I do know for sure is that every vault UUID must be unique within your account, and every item UUID must be unique within a vault. When we import from a file, we basically ignore the UUIDs. Brand new vaults get created, and then brand new items get created within those vaults, all with new randomly generate UUIDs. Internally, I believe that all we do is generate a random UUID, verify that it is in fact unique (within the necessary context), and regenerate if needed.
I don't know what your suite does, though. Could you explain your questions?