How to reproduce: Summon a named villager and a regular villager and a named cow:

/summon Villager ~ ~ ~ {CustomName:Dave}

/summon Villager

/summon Cow ~ ~ ~ {CustomName:Moo}

Then run

/say @e

Make sure you have debug tooltips enabled, then hover over the entries for the named cow and the regular villager, which should display their respective UUID. However, hovering over villager Dave's name will not display his UUID.