The answer to that is - lots. And lots care, because it's such an easy thing to check and get right. However there is nothing new in this, set designers and costume suppliers etc have been getting things wrong for a long time. In The Longest Day (1962) for example, they obviously couldn't decide which way the diagonal stripes on the DFC and AFC on Richard Burton's uniform should go, so they compromised and had the DFC stripes running one way and the AFC the other. Sure, lots of people wouldn't notice, but an awful lot would, including yours truly
TTN