lets clarify a bit the things.

If you never get a super rare with lucky rolls then at 1000 you get 1 of the super rares and at 2000 you get the other super rare with no chance to get dupes.

If you get a super rare out of a lucky roll (so before your 1000th draw) then the counter gets reset and since that moment onwards you are on a full new counter, is in this situation that you can get a dupe (the same if you get a 2nd super rare out of a lucky roll before your 2000th draw, if your 1st super rare was the fixed one you get for sure at 1000).