And therein lies the issue, how clear is clear?

For example, if someone managed to get hold of bottles with slightly thicker glass, you could sell a bottle of wine with slightly less wine in than is obvious from the outside, increasing the price per mililitre by a few percent. Not much individually, but it all adds up over the year.

If you’re buying that wine, and looking at a shelf of near identical looking shapes and sizes of bottle, you’re already factoring in grape, flavour, price per 750ml, provinence, alcohol content, etc, so what benefit do you get from one bottle being 750ml, and another being 736ml?

Standardisation simplifies manufacturing (of bottles) as well as purchasing of the end product by consumers. There is no benefit to an overly wide selection of sizes.

That sounds like a case for restricting the thickness of glass bottles rather than restricting the volume of liquid. How would switching to pints make any difference with that? As long as they’re labelled correctly I don’t see much problem.