Back in those days, Aix did not use the ELF binary model, rather IBM went their own path and imported the Windows concept of definition files and import libraries to generate shared objects.
Aix shared objects had more in common with Windows world than with other UNIX variants.
I've started with 5.1 therefore I can't relate to that.
Thanks for the answer, I got curious and decided to dive again into Aix docs, and apparently export files are still a thing.