The original question was:
... rate of no show passenger who have checked-in at the counter but do not appear at the boarding gate.
My GUESS is very few. On one occasions I was that 'Last call for Mr PaxBoy as we are waiting to depart" and with the (then) Mrs PB, we legged it to the gate. That was over 20 years ago and I have not done it since.
It is possible that some are repeat offenders but most will do it once and realise the problems they nearly caused for themself - they will tend to ignore the actual problems they caused others.
When watching UK programmes like 'Airport' [BBC] and 'Airline' [ITV] you you cannot be sure of how frequent a problem it is - because the programme has been edited to show you the juicy bits of people being late to the gate.
One of the few people in PPRuNe that could answer your question is
Bealine as he works on check-in and has been in the airline world for quite a while but he is absent from the forum at the moment. Perhaps send him a Private Message and see if he can help.