I actually managed to catch a repeat of the Celebrity Chase a couple of weeks ago that I hadn't seen before. Feel like now I've seen most editions at least twice.
Even pre-COVID though it seemed to be getting more common to have quiz shows sat on the shelf for quite some time before broadcast - and usually a question or two gives it away. I guess the more in demand the attached talent gets, the more it makes sense to film more episodes in fewer filming blocks.
There's a pre-COVID series of Celebrity Catchphrase that seems to have been filmed but not shown yet. I only know that because we got word at the charity I work earlier in the year that one of the celebs had chosen us to give their winnings to. However they're not in the line-up for the new series starting soon, so maybe sitting on the shelf for a while too.
The one I saw live in July 2016 wasn’t shown too late after, it had a Paralympic athlete as one of the contestants and from memory it aired in September during the Paralympic Games in Rio that year.
To my delight, Colin Baker from Doctor Who was also one of the contestants and absolutely stormed his round, an extremely clever chap.
It's been nice not having him crop up everywhere over the summer, though I think he has now stepped down from some of his roles on the daytime shows in order to concentrate on his own show.