Hello, based on this page from Tolkienbooks.net it appears that each impression has multiple "states," as I believe they would be called. My question is how does one determine one state from another? For example, I have a 5th impression of the UK TT of which there are three states. Are there slight differences between each or is there really no way of knowing?

https://tolkienbooks.net/php/lotr-print-runs.php

P.S. I understand that the answer to my question might lie within Tolkien: A Descriptive Bibliography, but alas I have yet to find a copy of that!