You can easy put some layers over the fiberglasstexture inside a mask..and that even years later.Thats a good idea if it smells still from the chemicals.Did that several times with lots of casts.And this hides the fiberglasstextures.But the glass is still there.
But it could also be a recast.But when an expert made the recast...you will see no difference to the real thing.
Can you bent the mask a little bit or is it extreme hard and solid?Fiberglass should be a little bit flexible if the mask is not casted too thick.Resin is rockhard and breaks very fast with too much power.