You can dry hop to replace previous "dry hops" that may have blown off, but AFAIK, there would be no science to how much to replace... I would not worry about it much, just my two cents.
If you are not growing your own 6th generation barley and hops, you're not *really* homebrewing.
Fermenting: Real Ale, Extract Lager (with WLP830), India Pale Ale
Drinking: Pale Ale from the keg