I've got a few really ancient clothes in my wardrobe. One of them is a pink wool dress which I wore in my teens. It's got a few small moth-holes in it, unfortunately, but I keep it anyway. Today, I tried on a skirt that my mother bought in a sale and never wore, who knows why. It's a size 10 and I've been using it as a yardstick of my size - a year ago I wouldn't have got into it. Today, for the first time, I could do up the zip and the waistband, though that was still a little tight.
Then I got out the pink dress. By no means wearable. I couldn't get it over my hips; that is, some of the way but not pulled down and I didn't even try the zip.
The skirt, which was bought ten or more years ago, is a size 10 and the dress, which dates from a couple of years either side of 1970 is a size 12.
I know that sizings get more and more generous - even at my largest, I found waists were being made far too big (I'm meaning by this, clothes that are meant to fit around your waist, I'm far too old to even want to risk the muffin top). This happened quite abruptly one year, when all the waists became a lot looser. And it seems that a 12 from 40 years ago is equivalent to an 8 now. Which seems a bit ridiculous.