Both my misunderstandings are entirely mine.

It is an interesting problem and one that is hard to specify in words. I just got caught up with trying to solve it using a generated regex and wasn't particularly concerned with keeping an eye on the rules, or even meeting their absolute requirements.

That's pretty much why I didn't publish my code initially. It is also quite a difficult problem to verify your solutions, given the variations in dictionaries etc. The only way I can see of validating is to cross reference with the original (deleted) problem and other peoples generated problems and solutions. I always left the possibility that my code was in error open when I posted questions/solutions.

Adding code to deal with this particular rule isn't a problem, but I have still to yet prevent my code from rejecting possible matches that contain duplicate, required letters. It may be that I won't find a (pure regex) solution to that task, but I am thoroughly enjoying the attempt. I learned a couple of new (to me) regex tricks already.

If my earlier suggestion that you re-write the rules to incorporate some of the separate assumptions into the base description, in an attempt to make the description clearer, came across as 'scolding', it wasn't indended to.

Thankyou for posting the challenge. I am (still) enjoying it. I wish we had more like this on a regular basis--preferably at weekends.