Here is some general information, since I do not know which purchase agreement forms were used nor what they may say. In CA, CAR forms state: Real Estate Brokers are not parties to the Agreement between Buyer and Seller. So all pertinent communications about the Agreement would need to be delivered to the buyer (or seller) as soon as practical. If the CAR "NOTICE TO BUYER TO PERFORM" was used, there is a "CONFIRMATION OF RECEIPT" which either the buyer or the authorized agent can initial. Your agent should send you a copy of the notice since you requested it, but the form does not have to be signed by the buyer. Notices to perform should be taken seriously and you as the client are ultimately responsible. Your agent should have been advising you on how to handle this and discussed any particular strategy he/she recommends. Your agent may be delaying the "personal receipt" of the notice to gain more time to comply, which is somewhat of a gray tactic, in my opinion. In any case, your agent should be keeping you in the loop about what's going on. You might want to talk with your Broker, the one your agent works for, and bring up your concerns.
I am a real estate broker qualified to advise you on California real estate matters, not the law. If you desire legal advice, consult with an attorney.
Hope this helps!