There's an anomaly in the Trooper/357 serial number ranges.
The 357 "stops" "around" 28000, but Trooper numbers don't "start" until 32401.
That's a pretty big gap, that's unexplained, but Colt did what they wanted without regard to anomalies.
My best guess would be a cleanup of 357-specific barrels before starting the Trooper-marked guns in this range.
To further complicate things, Colt also shared Trooper numbers with the Officer's Model Match in the 90000 range.
The only way you'll ever solve this is by either calling Colt and asking for a production date and model, or by spending the bucks on a Historical Letter.
Colt seems to be giving date and model info over the phone.
By the way, that's a beautiful 357 (you dirty #&*@#*) The one Colt I really wanted, and never found, was the 357. Back when I could afford Colt's, there was no internet and no 357's ever showed up locally.
Thanks, dfariswheel; maybe just out of curiosity, I will call Colt. I don't think it's worth big bucks for the history letter.
For some reason, those early .357s really appeal to me. This one, I nabbed at a local gun store just the other week: just the way I like to find 'em, about 98%, really nice, but not so pristine I don't mind doing what it's supposed to do, shoot!