I think 20% off on a Seamaster isn't such a superlative deal that you'd have cut your nose off to spite your face. That deal could probably be replicated via the greys.
If you'd turned down something like a Cartier Santos or another brand where discounts are verboten I'd say yes probably that wasn't a good move but in this case your money, you worked hard for it and if you want the full set at that price you should get it as you'd likely replicate that deal elsewhere.