I'm seeing this thread a little after the fact as I just opened a factory set and moved all my existing cards to extras. But I do notice that the factory set is 100% UNglossy, and the cards that I had previously were glossy #1-#279 and UNglossy #301-#500. I had no cards #280-#300 so I cannot vouch for them, but I am going to assume they were also released as glossy in the "Base Set". I note that comment exists for the Base Set in our database (not sure when it was added).
Two addditional observations regarding "Base Set" and "Factory Set". #1-#300 have "2008 UPPER DECK BASEBALL FIRST EDITION" on the back, while #301-500" have "2008 FIRST EDITION UPDATE BASEBALL". And this is true for all of the cards I have, whether glossy or not.
So wouldn't the "Factory Set" be #1-#500 matte finish and the "Base Set" be #1-#300 glossy finish? If there was an "Update" release available separately somehow (rack packs or hobby set or something), then wouldn't that be a separate "Update" set or something (like Score Rookie & Traded, or Topps Traded, etc.)?
--Kent