I just came across this and similar postings as I was reseaching the question, but see no definitive answers posted. Unfortunately the customer service desk is closed, today; however, it (now) seems pretty clear in my case that since my membership year ends on 8-Feb-04 (and my card expires 31-Mar-04), that I will need only 1200 tier points to retain gold for this upcoming (9-Feb-04/8-Feb-05) membership year. For me, that's an unexpected epiphany...if it's correct!
As you indicated, the BA website states that "[C]ards expiring from 30-Apr-04 onward will be renewed at the new...levels" and so you will need 1500. (In addition, the BA "Looking Ahead" booklet sent to us in mid-2003 confirms that "[t]he new renewal thresholds will take effect on 1-Mar-04 for existing Gold and Silver Tier members.")