The thing with writing is that it is hard to give a proper estimate of how long it will take.
I'm not talking about J R R Martin levels of delay, of course.
But youtube videos from professional writers seem to agree that most of the writing ends up removed or rewritten at some point before publishing.
And one of the hardest things to do when you are writing is chosing properly what to remove of the text.
And if something early needs to be removed or rewritten, later points may need to be changed to fit.
Add to that cbob clearly was going through depression and writer's block, and while we don't know what came first they clearly fed each other, good chances a part of the text was forced out and needs replacing.
I'm not saying they were not high-balling the 80%, but as that is for the script and not coding or art a big change like this is still likely.