It doesn't matter whether you've dropped a spark plug or not,
Check the gap with a gauge before installing them in the vehicle!
While 99.9% of spark plugs come properly pre-gapped, it is wise to take an extra second or two to check the gap for each plug against the recommended width with a spark plug gapping gauge.
Variety of common spark plug ...
I believe it is the "heat range" of the plug. That determines the temperature of the electrode in service. Changing the length of the center electrode affects how fast heat is conducted away from it. Long ago when many cars burned oil , a "hot" plug was recommended for a oil burner to burn carbon off the electrode.