"What was deemed safe engineering practice in the 1960s or even the 1980s might not be deemed safe today"
And getting back to the RJ isn't this the problem being faced today. Even ignoring all the excellent points being made about build standard, eng records, availability of documentation etc.
Is an aircraft designed tested and built to standards of the 60s/70s/80s (even if we assume that it was tested to, and fully met these standards) acceptably safe to bring into the inventory?