There's a thread on the bad place rn that I don't really want to get involved with, but I have thoughts on. Their point is that period costuming doesn't need to be historically accurate and inaccurate costuming shouldn't be assumed to mean the designer lacks knowledge. (This will be so disorganized)
This costumer has complained before about people who nitpick as a way to boost themselves up. I admit, I tend to take that as an accusation at me, which isn't fair of me - there's a whole world of monetized costube content on YT I know nothing about, and it's probably about influencers there.
At the same time, with no acknowledgement of the full spectrum of "people talking about historical accuracy of costumes on the internet," it's natural to assume that we're all being lumped in and condemned together. It would be nice to get that before the aggravated "well, I don't mean *you*."
Their point that inaccuracy doesn't mean ignorance is a very good one. I've made this point in reviews as well. There *is* a tendency among some to say anything inaccurate is bad, and that's not true, any more than fantasy is bad because it's not historical fiction.
BUT. There's a huge BUT. It doesn't logically follow that you need to assume that inaccuracies are never a result of confusion or misunderstanding, either. Especially if a costume designer says their designs *are* accurate when they're demonstrably not.
At a certain point, costume designers need to be treated like everyone else. Mistakes are made in every aspect of writing all the time, and people note them in reviews. It's not a condemnation of the mistake-maker as a human being.
Definitely don't harass the costumer to their face (wtf), but "I don't think they understand period construction because they used princess seams" is not an unreasonable thing to say. Nor is "they said only rich women wore hoop skirts in an interview, that's very wrong."