Like InspecterD said.... The last time I did "letter witnessing" we used the Kingdom Hall as a return address.  (Of course, though, we individually were footing the bill for the stationery, envelopes, and stamps!)

We had a list of addresses to write to.  At that time, it was common to go to the local library and use town records to find the names of the homeowners.  Nowadays, I'm sure people just go online.

So even if you're not in your local edition of the Yellow Pages, they may have found your name elsewhere.  That, or the letter was intended for you personally.  But I would think if that were the case, they would have been more specific in referring to your "coming back to the organization," whereas this sounds more like a generic letter.