Legal Question in Business Law in California

In general terms, if an offer is not accepted before it expires, then the offer dies and no contract can be formed.

If you can prove that the other party back-dated the agreement, and the writing is indeed interpreted as being an offer that expired on November 30, then no contract was formed. However, the issues of proof here may be extremely difficult, and I am NOT offering an opinion on your particular situation.

You may wish to consult with a lawyer, with whom you can discuss all the facts regarding the drafting, interpretation, and execution of the contract, and obtain his or her opinion on this question.

I agree with Mr. Perry. In a strict sense, the offer made by the contract document expired at midnight 11/30 and could not become a valid contract by acceptance thereafter. If, however, both parties act as though the contract is valid, and commence performance under its terms, they may find themselves bound by its terms under one or another of legal theories that allow enforcement to prevent injustice. For example, a court might find that there was a (unwritten) so-called "quasi-contract" or "contract implied in law," the terms of which were the same, or almost the same, as those contained in the written (but itself ineffective) document. If this goes to court, the judge may very well employ a quasi-contract theory to prevent injustice to one party or the other for performing under a contract he incorrectly though was valid.

I also agree with Mr. Perry on the difficulty of proof of the actual date of signing, especially if there were no witnesses present. Does the other party admit signing after the drop-dead date? When and how did the other party communicate the fact of his acceptance to you? In theory, one can often accept a contract in ways other than signing it -- as by beginning performance or by orally indicating agreement -- so I'd be somewhat cautious about complete reliance on the actual date of signing. However, if the contract is indeed quite explicit that it must be executed by 11/30, that would prevent a later execution from being excusable and the parties wouldn't be in contract (so back to the quasi-contract theory).

I'd urge the parties to get this resolved by negotiation or third-party mediation as early as possible, to avoid their costs and possible damages from getting out of hand. Involving someone with contract-law experience might be a good idea.

I see other issues in your post that the other attorneys do not address. One of those issues is whether there has been part performance. In some situations, such as a unilateral contract, the offer becomes irrevocable once performance has begun. This is a legal issue that may affect the outcome of any legal dispute between the parties.