The explanation offered by Murphydog might be correct. However, there is another possibility.
We don't really know when the Model 63 with no dash actually went out of production. Like Murphydog, I have never laid eyes on a Model 63-1, so far as I can remember. It is entirely possible that Model 63 production continued right up to the time the Model 63-3 was introduced in 1989. Keep in mind that the 63-2 was a Lew Horton special production gun, so it doesn't even count.
So, finding a 63 no-dash with a 1988 serial number on it comes as no surprise to me. I suspect there are lots of Model 63 Kit Guns around from the first 8 years of the 1980s.
The barrel pin went away c. 1982, but this would not necessarily have produced a new dash number. It didn't on some other models. The only indication we have that it did on the Model 63 is an unsubstantiated statement in the SCSW. It would not be the first mistake discovered in that excellent book.