How To Tell If An "Old Cleaning" Has Been Done?

Yes, if only because toning is a time-sensitive process. Aside the obvious kitchen artificial toners, the only time it's halfway easy to derive conclusions about toning is when it's just starting. Even then, you've got to have a pretty good idea of how natural toning progresses with that specific issue (Morgans don't tone the same way Buffs do, for instance). A retoned older cleaning is in many circumstances indistinguishable from one which wasn't cleaned, because the toning process took exactly the same steps either way. Is that an artificially-toned coin? Nope.

The only time I'll even consider toning as indicative of cleaning is if the degree of toning doesn't correlate with the age of the coin. I wouldn't expect a coin dated 1835 to look like it just started toning in the last three years. Even that, though, is iffy because there are plausible explanations for it.