You can check out scans of older versions of the rules from my site:
http://www.alanhoyle.com/ult-rules/
I have varying quality of scans of editions 1, 2, 3, 4, 6, 7, 8, 9, and 10
Unfortunately, the scans are not text-searchable, they are just images
7th Edition includes text "Players must play the disc, not the opponent. That is, they must not position themselves or move for the purpose of impeding other players. To do so is a foul."
8th Edition, the first UPA edition and a complete rewrite of the rules, is the first place that I see the word "pick" in XVIII.3.
-alan