Well I doubt if he has what he thinks he does. I have a Sears repair manual that states new for 62, featuring the 623 and 624 models also a 628, which replaced the old round hood. The frames are basically the same so you can mix and match them if you want. The only puzzling tractor to me is the 622, which was the first blue and white one, but also the last oval hooded one.
As far as having a manual dated for 1961, he might, as print date doesn't equal sale date, and since these were the new models for 62 it makes sense that some printed goods could have been done in late 61. I don't really know at what time of the yr new models came to the floor, I would guess maybe before Christmas so as not to miss any holiday sales. Someone told me once that the spring catalogs came out in Jan, so the earliest one might have gotten a tractor would have been feburary.