In defence of Mesa and the dealers, first shipment of any electronic product is always a movable feast. As a manufacturer, you plan for a specific first shipment date but that is based on each step from design, to full production running smoothly.
At Panasonic we would always do a pre-production run to test the production process, one month before full production. Any problems found on pre-production could lead to one or two month's delay in first shipment depeding on the severity of the problem. The products made made on the pre production run were used as demo samples. So there could be demonstration units around some 8-10 weeks before sale stock was available.
Of course each company is different but that is how it was at Panasonic when I was there.