at #ipres2025 @pwyatt explains that there is no one true PDF/A for a given content.
- there are infinite number of PDF/A possiblilites for any content
- anything can be made PDF/A - does not ensure it is a faithful representation

Vendors implement PDF/A conversion differently, so 5 different PDF/A conversions from diff software will likely give you 5 different files - all of them valid.