Smith and Wesson stopped pinning the barrels on their guns around 1982, give or take. The 66 no dash, and the 66-1 were the only two versions that were pinned. The 66-2 introduced non-pinned barrels for the 66.
This is also the time they stopped recessing the cylinder chambers on magnum guns and .22LR revolvers as well.
Pinned and recessed model 66's were only around for about 11-12 years, as compared to other models that were out for decades like 19s, 27s and 28s.
If you find a pinned and recessed 66 at a good price,cit is a must snag.
They are really, really going up in price though. People know what they have, and others really want them.