Look at it this way, they gave that specific address to the US post office because it is a good address for their mail to be forwarded to. And, if they are having mail forwarded there, then chances are that at least one individual who lives there knows who this defendant/respondent is (so that they can give them their mail). (Basically, the defendant did not just pick some address out of the air and give it to the post office.) Now, as a process server, you know as well as I do that many a times co-residents (and even neighbors) of defendants play dumb, and pretend like they have never heard of the defendant, in order to assist the defendant in evading service. As for not being on the association list of occupants, how up-to-date/correct/complete are those lists really? And, with regard to he/she not being the homeowner, well, I have a feeling you already know what I am going to say about that.
I am not telling you to necessarily follow what the agency is demanding of you--in fact, I commend you for being such an honest process server--but, I just want you to think about all of the reasons why service at this address may be okay.
As a final note, speaking from personal experience (in just the past couple of months!), these postal verifications more often than not properly point to the correct address for the party who cannot be found for service of process.
I agree with the other counsel, check the code as advised.
Legal disclaimer:This message does not constitute legal advice and does not create an attorney-client relationship. Any statements are made for general informational purposes and do not constitute legal advice. No attorney-client privilege is created by this communication. Attorney is licensed in California only.