One of the few things (the only?) thing about a character dying in angband, is that the next character using the same version inherits the monster (unique information). Therefor it makes sense to use a rod of probing on each monster (sub) type.

Currently, to determine which monsters have not been probed yet, I go to the Monster knowledge page (~e), select each category, select the first monster and repeat: right; check for "You know everything about this monster", left, down. Until the end of the list, then select the next category. This procedure is repetetive and because of that it is easy to miss a non-probed monster if you speed up the repeats too much.

Having some other way of finding non-probed monsters would be nice. Another entry in the "Display current knowledge" (~) might be overkill, but an extra column for each monster ( like the Ignore column of objects, displaying Yes or nothing) would help much, since then you only have to step (down, down, down,...) through the categories to see if there are any monsters without "Yes".

I would assume you could name the column Probed. Getting to know everything about a monster without actual probing (including its reaction to special attacks like disenchantment, chaos) is probably achievable, but in my experience unlikely.