Just remember that *most* (over 50% of) people were able to get a launch day delivery. Those in the latter part of the 4/245/8 window were too slow to purchase. These people are getting Watches that will only be manufactured in the coming weeks, whereas most of us are receiving Watches that were manufactured several months ago.
The watches that were manufactured "several months ago" (in other words three or more months ago) were pro-types. None of those are shipping to customers. Apple and in fact no company these days makes product that far in advance and stockpiles it. Three months ago the software wasn't even close to done. Maybe Apple ramped into full production and stockpiling a full month ago. But I doubt they stockpiled for more than six weeks.