Not an expert but I think the 2.5 inch J series lasted about 2 years. Not rare but not common.
I think they made a 638, 642 and 637 with that barrel length.
Some, If not all came with Crimson Trace grips.
The 2.5 inch just didn't show a big improvement over the standard 1 3/4" barrel and they had the lock. Then subcompact 9mm's came along and that was that.
I always found them neat but never bought one.
Enjoy it. It should be a good one.
Found a post using Google that said they were made from 2007 to 2009, for 18 months. A little later than I thought.
Also said as a plus the 2.5 inch barrel models provided a full ejector rod.
It also advised that there were 3 models as indicated above.