I doubt it really matters at all.
Quote from KentaKurodani:
How recent does a video have to be for a submission to be relevant?
I think the ultimate purpose for submission videos is to either show off a video with good (informative) commentary, and enough evidence that the run would be entertaining enough and marathon-friendly. It shouldn't hurt if it's an older run, and you have PB'd since then. as that is only more evidence that you have been/are currently improving your time. You'll have to prove that you have been practicing once the game has been selected anyway, so I'd go with one that you find informative and/or entertaining.