I don't think it's been proven 100% but so far I haven't seen or heard of anyone getting any 6 prop BS patterns or the top tier JC patterns from Acts 1 or 2 (not counting pony land, which is considered ~A4). Same with 5 prop/2nd tier Jc patterns in Act 1. I don't know what the drop rates are from act to act, like 5 prop rate in Act 2 vs Act 3, or even in any individual act. The only theory I've seen about their drops is that they drop in place of Tomes, but without a large sample size of rare patterns dropped, it's still just a rough theory.
Crusader DPS and EHP Spreadsheet, meant for Crusaders
My Wizard