Jac-
Unless a maker is being very honest AND very closely watching their suppliers, this is not unusual. Some buyers cut their sizes larger, to accomodate heavier layers. Some cut them larger to flatter customers ("Oh, I'm certainly not a XXL!") and then there's also the oldest game in the rag business.
Before laser cutters and computers, they made a brown kraft paper "pattern" for each piece of the clothing. The patterns goes to the actual contractor, who is supposed to stack up layers of cloth under the pattern and then faithfully cut the same outline in all of them, so they will be exact duplicates.
But may took the paper pattern, crumpled it up real tight,and flattened it out again. Except, it never quite goes back flat to the full original size. This is called "shrinking the maker" and it is a way that the lowest-bidder can use a little less cloth and make a little more profit with every garment. Cute, yes? (sigh)
And then in things like shoes, if you're vaguely "European", you'll find shoes and boots made in the EU, Italy, Romania...are made on lasts (molds) from real EU feet. In China and the pack rim? People and their feet are smaller, so "medium" becomes smaller, and proportioned differently.
Again, unless the brand name in charge is paying real close attention, or gives a damn.
All of which is why foulies really have to be tried on. (Unless you can convince Zappo's to sell them like the sell shoes, with free two-way shipping and a real trial period!)