This is a follow up to the question Can I cross out parts of a contract before signing it?
If a contract is given to someone and they modify it before signing, and the other party doesn't notice the modification until much latter (after both parties had full-filled/been full-filling their contractual obligations) would the part that had been modified be enforceable?
For example, if a manager emailed an prospective employee a contract containing the pay rate of $20/hr, if the prospective employee crossed out $20/hr and replaced it with $25/hr, then went to work and gave the manager the contract which he failed to carefully read, continued working for a few months, would the employee be entitled to $20/hr?
Since some contracts don't required a signature, what would count as the manager accepting the offer? I guess if it could some how be proven that the manager new the employee expected $25/hr and allowed him to continue work?