I don't think the changes affected the chance of dropping down really far. Only the ranking criteria were changed. As far as I know, selection works as follows:
1) Rank all the players
2) Put the top X of them into a pool (X might be 16, but is probably more)
3) Randomly pick one player from the pool, put that player into tournament 1 slot 1
4) Fill up the free pool slot with the next player in ranking order
5) Randomly pick a player for the next tournament slot
6) Repeat until everyone is assigned.
The change would have affected only step 1.
The chance to "survive" (drop down) one set of X drawings is roughly 1/e = 36.79%. If X were 16, the chance to drop 10 tournaments would be a bit better than 1 in 100,000. 20 tournaments, 1 in 10 billion. 30 tournaments... probably not in this universe

. If X is larger, the drop would be appropriately further - so for X=32, you could expect to drop down 20 tournaments with 1 in 100k plays. X=50, the 1 per 100k chance would give roughly 31 tournaments.
By the way, we could roughly determine X by observation if we knew the exact ranking formula and my selection algorithm conjecture is correct. Tournament 1 slot 1 must always be a player from the top X, so if we, for example, find the #42 ranked player in that slot, we'd know X is at least 42. If we were to find a player ranked 70 in tournament 2 slot 3 (19th drawn), we'd know X is at least 70-19+1 = 52.