Aha. I suspect some of these guys don't actually build the assemblies themselves, and/or don't do sufficient QC, and the product suffers as a result.
Cope did a 904 for my drag car a dozen or so years back. Received it with a park rod that was the wrong one.
After I got the correct one & swapped it in, the trans worked great and still does.
I chalked it up to parts-mixing and forgave it, but it mystified me nonetheless.