Contract Validity With Missing Effective Date

I would normally think that this would fall under a mistake and the effective date would be assumed to be the date that the contract was signed, but this is for an employment agreement and the former employer is now trying to enforce a non-compete and is actually suing for damages. Does their mistake in not explicitly stating the effective date of the agreement void it? The clause is below as it’s written in the agreement. Effective Date. This Agreement is effective as of [date]. Where necessary to carry out the intent of this Agreement, specific obligations under this Agreement wil continue after the date on which Employee may cease to be employed by Company.