I see a distinction with the language of the letter. Some will use the word "initial". All of them include a phrase "you have 30 days from this communication" or something like that. IMO, you could always play dumb if you get that letter and you think it is your first letter. Also, chances are the CA won't report until a month or so after you get that first letter.
I'd send the DV even if you are working out a written deal with the OC. The CA could decide to report anyway and a DV will also stall any action on their part, reporting included.
Haven't heard of PMAB, but a google search turned up a seemingly passive CA.