There seems to be a general misunderstanding on this sub about reanimation when it comes to units in reserved or deep strike.

Firstly, I think the confusion comes from units in reserve can now use and be affected by abilities. This is fine, units can use reanimation to heal wounds back if they are damaged.

However, if you read this section in the rules commentary about adding models back to units. It clearly explains it's not possible for two reasons

1. Models must be returned in coherency, can't be in coherency if not on the battlefield.

2. Models can be return to units IF they started the phase on the battlefield.

Since the reanimation occurs in command phase and units in reserve are NOT on the battlefield in the command phase. They cannot have models added to the unit.

That is all. Please read the following rules excerpt

Adding Models to a Unit: Some rules allow you to add models to a unit during the battle; such models must be set up in Unit Coherency with models in their unit that started that phase on the battlefield (i.e. models that were already on the battlefield when that rule was used). A model added to a unit during the battle can be set up within Engagement Range of one or more enemy units, but only if those enemy units are already within Engagement Range of the unit that model is being added to. When adding models to a unit as described above, any models that cannot be set up due to insufficient space are considered to have been destroyed, but do not trigger any rules that are triggered when a model is destroyed.