1st thing i am curious about is why you sold this work at all?, 35 houses out of an estate of 40 sounds like a great bit of work!.
But as to your question, given the time frame involved, no i dont think you are doing anything wrong. You sold the guy this work, it is up to him to keep the customers by doing the work to their expected standards. If he has not done this, that is his problem. If it was within a year or two, i might be inclined to get back in touch with the guy, but 6 years?, get in there!.