It’s a really grey area, I agree.

Lord Denning, a famous British judge, was the one who first addressed the so-called “battle of the forms” (this issue).

He went so far as to say you’d have to make changes in bright red ink with big arrows pointing to the changes made while telling the other party that you made them. He thought that people trying to be sneaky were acting immorally, and that it violated the spirit of contracts, which is to have a mutual agreement to be bound by obligations.

But if you can lead evidence that a reasonable person ought to have known/read the document, then you can validate the contract even if the other party finds out they screwed up.

Then they have access to other potential equitable remedies, like the doctrine of unconscionability.