So in your case where you have a very dense layer that you must drive through to get to a desired bearing stratum, you might have to deliver hard hitting blows to a point where you are getting pile stresses approaching 0.9Fy (which requires a PDA to determine). If the pile stops moving then you have hit true refusal. You tell you have hit refusal because the pile isn't moving anymore.
Specifications should provide some guidance as when to stop the pile driving in order to protect the pile from bad inspectors and contractors. Most of what I have seen is 10 blows for 1/2" or less or 20" for 1", but you can tell its on hard bedrock before you get to 10 blows... and in some cases the inspector may want to call it before its reaches that point. The ram has a tendency to bounce higher and higher after each blow when the pile is sitting on something truely hard. The higher the ram goes, the harder the pile gets hit, the closer you get to exceeding the yield strength of the steel pile. It is very important that the inspector is on top of their game when the pile reaches bedrock.
As a side note, piles driven to a softer bedrock may gradually "fetch up" to get to the 10blows/0.5" so there is less concern of overstressing the pile unless your inspector is terrible. In my field days, I did see piles refuse on very large boulders nested in glacial till... so keep that in mind.