Despite numerous trips into the past, the future, and alternate presents (and alternate pasts and alternate futures), the Star Trek timeline usually managed to get wiped clean and put back where it belonged at the end of the day.
That all changed with J.J. Abrams's take on the series. This remake? reboot? prequel? sequel? ...whatever it was, it featured Leonard Nimoy's Spock from the classic timeline time-traveling back into the Zachary Quinto Spock's present where the destruction of Vulcan creates an entire new Star Trek timeline that also fits with the continuity of the old timeline. So now there are two canon Spocks, but they each have different histories. Or the same histories but at different times. Or something like that.
