This very Collection
Early on (no date) ~ 600 cards
With onset of Season 2 it experienced a strong growth, first dated numbers:
Mar 03: about 5000 + bidding on more than 10k cards
Mar 10: almost 7000 cards, still bidding on more than 14k (and thousands more on the list).
Mar 15: over 8000 + bidding (or owning) all ~20.6k S2 commons
Mar 22: Over 10000 cards now, most S2 uncommons also bids on ... rest and rares + S1 ..pending
Mar 28: almost 12000 cards and bidding on another 17000+ cards: all S2 cards default flag I know of and some S1 as well
Apr 07: less increase, about 13500 cards (last 1400 not yet added, oops)
Apr 11: all cards (hopefully) included since the last collection-update 11 days ago. About 2000 cards, making a total of over 14000 cards now. Still so few S1 cards, well.
I need more bank to add the Season 1 cards. Those tend to be expensive if they are present..