I disagree. If cards are known to be stolen or printed beyond company defined print runs, there is always a large risk that, in the future, a way to discern a difference might be uncovered.
I recall Steve Taft discussing how specific sets and the 1986 Star cards being reprinted or outright unauthorized runs, however, you seem to be saying that employees also printed 1983-1985 cards. That is a problem, if true.
Technically, such information could cause the Star cards to be deemed unlicensed, since the employee ones would not have been accounted for in contracts.
Beyond that, the rumor used to be that someone purchased (stole?) the plates/paper/inks at auction (warehouse liquidation? dumpster dive?) and created new cards.
If Star never bothered to destroy/deface the plates and proofs, it causes authentication of legitimate issues to be more difficult.
PSA guarantees their grades. I’m not exactly certain this includes guaranteeing authenticity. For some reason, although common sense would imply it does, legally, it may not. By contrast, CSG/CGC (much like SGC when CCG owned them) financially guarantees authenticity of cards they grade. If, at some point, a way is discovered to discern official and unofficial print runs for Star, it might leave CCG open to liability that they simply don’t want their shareholders to bear.
Given Star Co issues are nearly four decades old at this point, there is no real financial incentive to accept the risk on this situation.