Firstly, apologies as I don't have a scanner to hand right now and I only just discovered this. On page 19 of the "Star Wars Vault" book there is a photograph taken at the 1976 Worldcon of the Vader suit, 3PO and an R2.

Anyway...the picture clearly shows a handwritten sign next to Vader saying 'DARTH VADER - TEST MOCK-UP' what is interesting is that inner robe is tucked under the chest armour.

So, I can't find a date for the 1976 Worldcon but I am presuming it took place post ANH shoot and that this is the movie suit that was sent after the last days shooting from ELstree. Otherwise, a full suit made its way to the US before the film had even started shooting. (Which I can't quite believe)

Anyone have any definite answers or info?

cheers

Summer of 1976 in Kansas City.

Source: http://theswca.com/relics/prerelease/