So here's a thought... since these cars might have sat for so long, not running, perhaps the compressor seals did let some of the R134a leak out? Those seals are designed around a turning shaft, which keeps them coated in oil. If they sit for a long time, historically, they could develop leaks.
For those with underwhelming ac performance, try this: Start the car, set the climatronic to MAX AC, turn the interior fan speed down to the 1st or 2nd setting. Go under the hood and feel the suction line at the compressor. It'll be the bigger of the 2 lines. After a little bit of running it should be COLD. If it isn't, that means either the compressor isn't pumping enough (bad RCV), or the system is low on charge. (bad radiator fans would cause this too, but I'll presume those are working and the condenser isn't plugged full of crap since these are "new" cars)
You can also log into the climate control head with VCDS and monitor the compressor request. Here's a view from our Touareg, you should be able to find similar values:
Note the Compressor Current, and Compressor Control fields. I took that screen shot with the HVAC set at minimum temp and max fan, on a hot day with the doors open. Under more normal circumstances those numbers will come down once the system "catches up" to the load. If they stay pegged out, that is another indication that either the charge is low, or the compressor control isn't working properly.
-J