Accepting partial rent after serving Notice to Vacate

[Michael W.]

This is my first time evicting a tenant. This relates to a commercial (retail) building in CA.

On 11/6, I served a delinquent tenant with a  3-day notice to pay or quit. Tenant requested that I give him until 12/15 to pay back rent and late fees, which I agreed to. However, on November 15, I served a 30-day notice to vacate and told him that if he paid everything he owed by 12/15, I might void the notice to vacate. 

The 3-day and 30-day notices were served (substitute service) on his business partner (the store manager who is not named on the lease) rather than the leaseholder, who was absent both times. For the 3-day notice, a separate copy was mailed to the leaseholder at the tenant's business address, but this wasn't done for the 30-day notice. I completed a Proof of Service form for both notices.

Is the 3-day notice still valid and I can go ahead and file an UD complaint using it as proof of service? Or is it considered to be "overridden" by the 30 day-notice that was later served, which could be ruled invalid since I did not mail a separate copy to tenant?

Tenant failed to pay by the 12/15 deadline and I now wish to file a UD complaint. However, the leaseholder is claiming that he never received any notices. I told him they were served on his partner. As long as I have a completed Proof of Service form, will any claim that he was never served be rejected by the court?

He also agreed to pay 50% of the back rent. Is there any downside to accepting a partial rent payment after serving a notice to pay or quit but before an unlawful detainer has been filed?