In a fairly recent thread about Mudcat history, it was noted that the filter only returns about 100 results, so if there are a hundred more recent ones than the one you want, it may be "found but not displayed" a.la. Google general web searches.

Often, if you remember a name of someone who participated in a thread you want, searching for "posts by ..." (easy way: clicking the name in another thread) is a productive method. It helps when you use this method if you can remember approximately when you last saw the thread you want, so you can apply an "optical filter" in the near time-span.

("optical search," or "optical filtering" is also known as "eyeball it till something pops out at you.")

John