I would like to know when a particular definition for a mathematical object was reformulated into the new version. Is there a place on stack exchange for this?
If not, then where would I go for this info?
I don't see why you would not ask this here.
To add to Mariano's answer, keep in mind that there is a tag for math history questions: math-history.
You may ask questions about the history of mathematics at History of Science and Mathematics Stack Exchange, which is currently in beta.