The istari that succeeded

[Legolas]

The time of the Istari's arrivals is only given once, so we're only given one option to believe. We also see a quote in The Silmarillion:

Even as the first shadows were felt in Mirkwood there appeared in the west of Middle-earth the Istari, whom Men called the Wizards.

I used 'canonical' in the sense of which writing takes precendence. On the matter of what happened to them, we're given two thoughts, so it's cloudy on which was intended and which we should believe