Looking at Tesla website at the different vehicles available in stock. There is a s 75d used that says 0-100 5.8sec. And a new 75d that says 0-100 4.4 sec. Is this the software unlock and could the used one get upgraded.
Yes, its called uncorking. Most S75Ds can be uncorked. You'll find with a full battery it's a bit quicker than 4.4 seconds too, more like 4.0-4.2.
The drive units were updated though in June of 2017. We have yet to uncover what was done but it was significant enough to change the option code.
It's also hard to tell if one can be updated. I have a Model S 75D manufactured in Nov 2016. It's one of the first with AP2 and new nose cone etc. It just recently had the "uncorking" done at service and is now a (approx) 4.4 0-100kmh car (equivalent of the USA 4.2 second 0-60mph). I'd suggest getting Tesla to confirm if the 5.8 car can be uncorked before purchasing if it's important to you. Shane.
Mine was uncorkable with VIN 1517XX, built Aug 2016. Very noticable increase in performance, and at full charge I get about 4.2s 0-100kph.
Has the Melbourne service center uncorked other cars not on the original approved VIN list? Are you sure they know how to determine eligibility?