Daikin VRVIII Short of refrigerant?

[Tayters]

I'd have done the same, ran just the faulty units on their own to see what they do. Haven't got a checker so would have to do it the long way but would go something like:
Getting to the EEV and unscrewing the head to see if that makes a difference.
Try all units in heating to see what they do.
If it's a 3 pipe system then the changeover box has a 4wv in it. Crud idea really. Get a service manual and check the pipe diagram to figure the circuit. Have only ever seen them stick in heating. Yours would have to be stuck halfway so could rule that out for now I suppose.
Reclaim would probably take a couple of hours, perhaps not to bleed it dry but enough to tell if you are short or not.
If the customer thinks they are more important than they guy fixing the AC leave it on test heat a bit longer.

Cheers,
Andy.