I used to own a fibreglass manufacturing company...we produced everything from repro fenders, bus body panels, Foden and Mac truck panels, boat, caravans beach buggies to commercail air conditioning ducts.
The quality of the product depends on several things
1/the quailty of the orginal plug
2/The stiffness of the moulds
3/The skill on the guys on the chopper gun and the guys rolling out
4/ How the units are braced in the moulds before release
5/how fast the units are popped out of the moulds
6/Moulds do wrarp over time...we used to get 60 to 150 units from a mould, depending on the accrucy the customer required...some units like horse float roofs that could not be seen on top did not require the same finish.
The main issue with fiberglass is manufacturers pushing limits beyond the real lifetime of the moulds....making quality plugs/moulds is time comsuming and expensive.
Hence maybe the reason of comments above...re a unit obtained yrs ago and a recent on.
Fixing a warped unit....this can be done, but requires a lot of work...usually involving cutting and reshaping before even looking at any high and low areas.
Most of these can be 'pulled' out during the reshaping..