Re: Dress length
This is from 1868 -so a bit earlier than us - but from what I can see the requirements hadn't changed much


Its from Harpers Bazar in 1868

It goes up to 16 presumable because girls were coming out at 17+. I would have guessed our PSYR girls would wear debutante length dresses even though they are not technically had their coming outs -unless we count the Hogwarts one as the official dress length drop moment.

I was a boarding school girl and they would measure our skirt lengths with rulers to make sure we were keeping to correct lengths - because different years were allowed different lengths - I'd always sort of thought that uniform letter would indicate dress length and matrons would check - strictness of matron determining if she just sort of eyeballs it or goes as far as measuring.
Or uniforms could be charmed to drop the hem automatically when a girl reaches a certain age.

I sort of thought that the basic dress part of the uniform would be written generically like 'plain black dress (X) hem' - that way poor girls would have a basic black cotton dress, while richer girls might be in better tailored or better quality fabrics - with then the official robe bit over the top. I admit this is based almost entirely on A little Princess! lol

Edit: posting a discussion of girls dress lengths felt weird from murocks account....so i changed it