There were a number of reasons for high-score "rejection" back in the day, so to speak.
As you may be aware, after every honor score, local association officials were required to make a full inspection, and that inspection included lane conditions, pins, ball and other factors. And non-compliance with ABC/WIBC rules in any of those categories would be potential reason(s) for disqualification of high-score approval.
Without a doubt, a very large percentage of the rejected scores were because of non-complying lane conditions, but there were a few disqualifications because of other things as well.
[Fast-forward to the 2000s, when several 900 series were approved, even when bowled in unwitnessed prebowling sessions. Have times changed, or what?]