Only a guess Tim. Remington, like the other US makers, imported raw tubes with the joining, fit and finish here. 2 (or less commonly 3) segments were used, with the thicker segment at the breech. All the 1900 KDs that I've seen use 'Oxford 2 S.J.', the large scroll coarse leaf asymmetric crolle found on the breech of those barrels. The fact that the barrel finisher joined segments of 'Boston 2 S.J.' to both barrels, which are mirror images of each other, suggests this was not a mistake, but possibly sample barrels to demonstrate the available patterns? It should be noted though that until the barrels are finished, the pattern is quite difficult to discern. You've seen the discussions on the PGCA site about the 'D' codes maybe being used to help the finisher grab the correct barrels for the grade.
http://www.picturetrail.com/sfx/album/view/19025099 This is Doug Miller's W. Moore with two different Laminated Steel patterns, the thicker at the breach. The patterns join in a straight line weld suggesting that the barrels were formed as tubes then one tube flared, the other coned and butt welded together.
Here's an 8 gauge LC Smith with two different Chain patterns
We've seen this Bell Brothers with fluid steel and damascus barrels
