Repairing the Never Healing?

[PvK]

Could someone please explain to me roughly how units with the "Never Heals" trait are repaired. For example, I brought a beat-up commander leading a bunch of beat-up units, both of which have the "Never Heals" trait, to a province with a lab. It seems like a random number of them get a random number of hit points repaired each turn. Two turns after they arrived at the lab, the commander and two of the units are still not repaired, but the others are.

Since it's hit-point damage and not afflictions, is there any way to check their repair state without examining each unit's details individually?

Is it just random? If so, does anyone know how what the odds are like?

PvK