In theory it sounds like a good idea, but it isn't possible in Accordance. Adding a field presupposes there is content to search for. These dates are in a table in CNTTS, and so yes, are searchable. But there is nothing to link those dates with manuscripts except the hyperlinks we create. We can't search inside a hyperlink; it merely points to a location elsewhere in the resource. Theoretically we would need to tag each manuscript with some sort of hidden date metadata that could be searched though it is not actual content - and this defies the entire paradigm of searching tools in Accordance since everything you search for is actually indexed and displayed in the module itself.
Even then, as Matthew pointed out, the dates are often ranges or approximations, so searching them becomes potentially convoluted.
The best workaround I can think of (and others are free to chime in as well) is to create some sort of saved list that you then paste into the search bar in a parenthesized list.
The other one is old school; use and study TC more and you will begin to recognize which manuscripts are earlier, later, mostly fragmentary, etc.
Anyway, I hope this helps to think through the process and let you see that we do read requests and think through them as well! (at least when it relates to a research focus of mine )