VerifyGCType is a flag to control during which pauses to do verification.

Verification before and after young collection checks this flag only for the "main" bulk of verification, not others.

Eg. from G1CollectedHeap::verify_before_young_collection:

void G1CollectedHeap::verify_before_young_collection(G1HeapVerifier::G1VerifyType type) {
  if (!VerifyBeforeGC) {
    return;
  }
  Ticks start = Ticks::now();
  _verifier->verify_region_sets_optional();
  _verifier->verify_dirty_young_regions();
  if (VerifyRememberedSets) {
    log_info(gc, verify)("[Verifying RemSets before GC]");
    VerifyRegionRemSetClosure v_cl;
    heap_region_iterate(&v_cl);
  }
  _verifier->verify_before_gc(type); <---- !!!! only this call honors verification type
  _verifier->check_bitmaps("GC Start");
  verify_numa_regions("GC Start");
  phase_times()->record_verify_before_time_ms((Ticks::now() - start).seconds() * MILLIUNITS);

Only the marked call honors the verification type. Everything else is executed unconditionally when VerifyBeforeGC is enabled. Similar with VerifyAfterGC.