...is mid-1971. The USAC Champ Car season ended in October in 1971, so it would make sense to attribute the watch to the second year of the engraving rather than the first.

And though teams then would have been in the tens rather than the hundreds of a current top-line F1 team, I agree there's nothing to point to it being Unser's watch rather than a less-decorated member of the team. And that value looks to be pitching it as driver-owned rather than, say, an engineer. No reason to think the engraving wasn't contemporary but it sure doesn't look like they got the best engraver money could buy!