For me there are a number of issues.

First, the document should be consistent, and whatever is allowed or not
allowed in one section should apply in the other.

Given that, we need also to consider whether we are talking about an active
or passive area of the substrate; in other words, is there circuitry
involved or not.

I have no problems with solder resist skips or missing segments if they are
in a passive area of the board.  I always have problems with exposure due
to scratching or mis-handling, as this is indicative of process loss of
control.

Obviously there can be no missing mask when there is any possibility of
either bridging or shorting.

I hope this helps, but we still don't have numbers.

Lionel Fullwood.