The point previously made about whether the agreement has been signed or is still in draft form is important;, as is the recommendation to engage a local attorney who is experienced with assisting in separation agreements and severance negotiation. Your question, "what are my rights" should be expanded to "what are my options and negotiation leverage" and I think you need to get those answers from your attorney. I hope it works out for you.
THIS IS A GENERAL ANSWER TO A GENERAL QUESTION AND SHOULD NOT BE RELIED UPON AS A FULL LEGAL ANALYSIS OF ANY FACTUAL MATTER. An attorney-client relationship is not established or offered solely as a result of this answer.
Your best option is to have a local employment attorney review the agreement, particularly if you have not yet signed the agreement. Severance agreements are generally drafted by attorneys for the employer and are designed to protect the employer, not the employee. Given the mistakes that seem to have been made, it wouldn't hurt to have an experienced employment attorney review the entire document. Try the Find A Lawyer tool on Avvo, the National Employment Lawyers Association website, or the California Employment Lawyers Association website. Good luck.
A lawyer would need to analyze the various versions of the agreement, related correspondence, and relevant facts to render an opinion - and even then, that opinion might not be definitive (mistakes make for murky fact situations).
It appears that there is enough at stake to justify your retaining an employment lawyer to represent you. Good luck.
This information does not constitute legal advice and does not establish an attorney-client relationship.
The bigger question is, "Have you signed the severance agreement?" If not, consult with an employment attorney who can review and discuss negotiating the terms with your former employer. An attorney will usually charge an hourly fee for these services. If you have already signed it and they are not abiding by the terms, it is too late to negotiate the terms, but it is not too late to discuss a breach of contract action with a civil litigator. Good luck to you.
Lesly J. Adams has been licensed to practice law in California since 2010. The information presented here is general in nature and is not intended, nor should be construed, as legal advice for a particular case. This posting does not create any attorney-client relationship with the author. For specific advice about your particular situation, consult with your own attorney.