I ordered 4 1950S dress from here. (order FD*******) One of them turned out to be out of stock, but the seven other were delivered home in France 6 days later, which is a pretty good performance from Hong Kong.
Unfortunately, the 7 shirts were too small. There is indeed something strange with the RetroStage size code, as I had ordered 3XL and 4XL sizes using their guide, when my usual size is a standard European XL, and despite this their 3XL and 4XL sizes were too small.
I hence filed a ticket with their customer support system, and I must admit their response was quick and very helpful.
I had proposed to return the shirts for an exchange. Their answer was I was to keep the shirts and they would still refund 50% of the order, which I thought was a pretty decent deal since I had indeed ordered the wrong size to begin with.
So as a summary, be careful with the size codes, but RetroStage is a reliable on-line supplier.