I don't consider it ambiguous. The key part of the wording is "on day with most finds". So if you get 50 caches in a day , and then later you get 51 in a day, then the latter is used for the points, and the first date is ignored.
As for getting 200 in a day, then yes it's a challenge, but getting 40 belt points isn't meant to be easy! If you do ad-lab caches, then getting 200 in a big city like London is probably achievable. For what it's worth, my maximum in a day is 100, but then I don't do ad labs.