They are bringing back an old game, after all. The fans and the way in which they are/can do it means entirely new figure ranges are not an option.
It would be cheap and easy for them to replace centrifuge moulds if there are any issues, as I'd assume they kept the tins/master moulds.
The moulds for injection can wear and have issues, but can be repaired also.
I would doubt there would be any visible issues. They appear to still have the original dates on the sprues, so that would suggest the original moulds.
I would doubt they would release figures with obvious issues. PS Finecast! Doh! But that's exactly why they wouldn't want a repeat.
They have adjusted some metal figures to be more appropriate for resin casting, refining details. But this may also suggest the loss of the tins or master mould that made them.
Due to the nature of rereleasing ranges that were originally endlessly tacked on, tacked on over many decades, there is of course variation in quality/style.
The only other option would have been complete overhaul that would be costly and only put off fans.
It is good that they are releasing so many figures. The orcs have loads available, older, newer, brand new, and real old. Something for everyone, whilst producing a cost effective rerelease of the universe.
The problem with the new stuff like AOS is all the fragile sticky hooky bits that are a pain all around.
WFB had a style that is less difficult. The sprues were easier to deal with as well as being nicely spaced out with arranged pieces that you can actually get a tool inbetween.