I think that's not true of @HenryT 's 2015 Model S - it certainly isn't of my 2014 model. I think the change came in with the facelift and the switch to the Model X charger (max 24A 3-phase), but I am not 100% sure and there might have been an intermediate variation.
Certainly early EU Model S had in effect 3 16A, single phase charging modules, or 6 of them if you ordered the 'dual charger' extra-cost option. The base model could charge from 32A single phase using the UMC, because the UMC blue commando adaptor bridged the three phase pins together; these cars could only charge at 16A from a standard 32A single-phase chargepoint. That was just about tolerable in mainland EU where domestic 3-phase is more common (and domestic high-current single phase rare), but in the UK with the OLEV scheme meaning that most people would have a free 32A chargepoint at home it was a significant problem. Just before launch in the UK, Tesla and Chargemaster flirted briefly with a plan involving Chargemaster units with the phases bridged, but it was rapidly realised this was a bad idea (such chargepoints blow up Renault Zoes for example), so the modified chargepoints were withdrawn and Tesla fitted all UK-delivered Model S with dual chargers whether you had ordered them or not. Somewhat later, a software kludge was implemented that stopped you charging faster than 16A on three-phase unless you had paid for the second charger.
So on this generation of Model S (unlike later Model S or Model 3 etc) there is no switching hardware to fail and result in a 16A limit. It is of course possible for the second charger to fail or for the software limiting kludge to have gone wrong. I wonder if Henry's car has the 2nd charger paid for.
Thanks for your time and trouble in explaining that Arg, though I'm afraid some of it I'm struggling to follow.
I don't have a clue if I have the second charger, to be honest. I can't say I've seen it mentioned anywhere but not sure I'd have noticed if I did. I bought the car used in Jan last year so don't have the original papers (if there were any).
Charged the car today on a public charger and as expected the car drew 32A - didn't have the time to set it up as a timed charge so just plugged in and got 32A, just as I do at home.