I'd wager your saddle is original. The Terry mattress saddles were popular in the 30's - It seems that by the 50's their popularity faded. (At least most of the pics that I have seen of post-war roadster-type bikes show they were equipped with leather saddles).






Also - the rear mudguard white-tail was a new safety reg circa 1934, so I'd surmise that your bike was built late 30's or 40s.