In the cases of Poirot and Holmes, both series are, I believe, exhaustive. That is, they filmed every story in the respective canons. As someone mentions above, the Poirot may not be quite as faithful, but AIUI, the Holmes series is about as faithful as could be desired. This level of fidelity to the source material and completism is very unusual in television production.
For instance, the popular Father Brown series bears almost no resemblance to any of the Chesterton stories, beyond the presence of a somewhat pudgy Catholic priest named Brown who solves crimes. It’s been a while since I read them, and I may not have read every one, but I have recently watched the full run of the show. I don’t believe Chesterton wrote the characters of Mrs McCarthy or Lady Felicia, or any of the other regulars in the show. If he did, I don’t think they appear in many of the stories.
The only other similarity I can recall is the jewel thief Flambeau, who in the stories is a former crook, now friend of Father Brown, where in the show he is a sort of frenemy, but still actively thieving. (Someone who is more conversant with the full Father Brown oeuvre can correct me if I’ve forgotten other similarities, and certainly will, if I know my fellow Dopers.)
The Chesterton stories are also not all plotted as neatly or as conventionally as the show. Often the story just stops dead with Brown’s explanation of whodunit, with no followup. We don’t see the apprehension of the criminal, or any other tidying up of loose threads.
The Jeeves and Wooster series was not exhaustive. There are only 23 episodes of the show, and according to Wikipedia, Wodehouse wrote 35 short stories and 11 novels featuring the pair.
But although I love most of Wodehouse’s stuff (except the stories that center on golf or cricket, sports I don’t know – or care – anything about), even his most devoted fans have to admit that his plot lines were a bit repetitive. An inordinately large percentage of them have to do with the hero, whether Bertie or someone else, trying to get out of an engagement of marriage he has somehow blundered into.
So it was probably pointless to even attempt to do an exhaustive Jeeves and Wooster. In fact, you could probably just copy and rename an episode and have Stephen and Hugh overdub the names of the girls in question, and tickety-boo, there’s another story checked off.