<Updated the whole description, Clarified some things, and rewrote my report>
I noticed that the character limit for book titles in 1.20.2 is 15 though they were 16 previously, after some investigation I found this bug going back to 20w17a (1.16 Snapshot) with no mentions in the changelog. Hence this was obviously not intended I kept this report up. To sort out some confusion, I had a typo in my first submission that misspelled 1.20.1 to 1.12.1 which raised obvious confusion, I hope this resolves that. 
Furthermore if this issue is recognized and tackled I suggest the limit being raised, as it makes no sense that I can rename the book in an anvil with 50 characters, but cannot sign it with a 50 character title, also copying/pasting text and moving the cursor in the menu would create some parity to writing in the book itself, editing the title/item name in an anvil, and recent changes to signs.

I want to apologize if I was a bit rude in the comments, I did not intend to offend anyone for being confused about my typo.
Let's get this behind us and make this game better by removing 1 bug at a time