Does CV halve immediately if unit is isolated?

[helios123]

At 30.9.5: Isolated units have their display CV halved, but in practice their CV only drops slowly. So the first turn of
Isolation their actual CV will be higher than suggested, while after a few turns or it will begin to drop.

But the manual also says at 23.14.4: Isolated Unit Combat Value Penalties When a unit is isolated, the CV value in combat divided by 2.

So which is it, does an isolated unit have its actual CV halved immediately or only after a few turns?

In general how effective do you guys feel is it to wait a few turns before attacking isolated units (presuming also you limit their resupply from Air/Sea.

[Jango32]

It is immediately applied. As soon as a unit is considered isolated at the start of a turn, pound on it.

[Shiva the Destroyer]

It is immediately applied. As soon as a unit is considered isolated at the start of a turn, pound on it.

In 1941, you are somewhat correct since

11.3.5. Air resupply
For all turns in June 1941 air resupply cannot be used to prevent isolation of Soviet units no matter how much is dropped (25.9.3). This will take effect normally for any such missions run in the Soviet T3 (so will not affect the Axis T3 where such units will remain isolated).

but in turns other than June 1941 if the unit(s) happen to be air resupplied then 23.14.3 applies

23.14.3. Isolation and Air-Resupply
A unit at the end of its turn that can trace to depots that have received a combined total of 500 or more tons of freight during the turn will be considered in supply (not isolated) during the enemy player’s turn. This allows air resupply to prevent units from facing isolation penalties when defending in combat, however, they will still be considered isolated during their player turn (when they might attack for example)

[Jango32]

Right, but that is only if at least 500 freight via air supply is received. Preexisting freight is irrelevant. I suppose it's true on a technicality, but you should still immediately attack regardless of the CV penalty existing or not.