Killing delve boss Sargos Grent in Echo Crest and killing delve boss Cynaceae the Verdant in Kingscrest Cavern did not count as delve boss for the daily kill 2 delve bosses endeavor. However, killing delve bosses Longfang and Hegris the Black Dagger in Breakneck Cave counted as 1 delve boss for the endeavor. So I completed three different delves in Cyrodiil today, and got credit for one on the daily endeavor. However, all three counted as new Explorer achievements for the Cyrodiil Cave Delver achievement. Left Cyrodiil, went to the first delve I found, killed the delve boss, and finished the daily endeavor.

Separately, does anyone have a complete list of the delve/delve boss in Cyrodiil that do not count for daily endeavor kill 2 delve bosses?