I myself lost the contact details of a customer who had ordered a knife. He hadn't paid yet, but a lot happened in between his order, his knife never being made 'cos I couldn't confirm the details and finally meeting up with him again a year later at a knife show. I kinda figured he would be there and he made a bit of a joke about it - he was good about it all. All in all, there didn't seem much urgency in it since he never actually contacted me either - he did have my details. But the funny thing was that he had come to expect that makers take their time and an estimated delivery time is no more than a rough guess which could be off by a couple of years !!
But seriously, most makers, being part-time, often have "other" pesky jobs, committments that need more attention than the knifemaking. Often there are ongoing or sudden problems like illness, injuries, relationships, breakups, new child, gone bankrupt, house burned down, who knows - gone to jail, even died ???
Having said that, nothing beats good correspondence and a realistic outlook. (From both parties.) Emails and quick letters, notes, phone calls, and updates, should receive a portion of a knifemaker's schedule, as should research, trying new techniques, going to knife shows, getting together with other knifemakers to talk shop etc.
I'd guess that most people would much prefer to KNOW that their project has gone down the drain, or the maker realises he can't do it. Can't get the materials for another 6months, has run out of gas for the forge etc. Its better to know than to wonder aimlessly and perhaps get that little bit paranoid, especially if money has already changed hands.
Some makers who have 2 year waits (or even 15years in a couple of cases), still take orders because those guys placing orders are willing to wait that long. I'd assume that there was some kind of understanding there.
My 2 cents worth. Jason.