I think we agree that Sheaffer imprints often included numbers indicating the price of the pen or pencil, e.g., 1000 = $10.00. Attached is a shot, albeit not that skillful, of imprints on identical Sheaffer Crest Tuckaways in blue. Both have identical caps, triumph nibs and white dots on the bottom of the barrel (end of the blind cap). The bottom pen has a 1500 imprint and the top has 1750.
The only difference I can find between the two is that the 1750 pen has about a 1/4" portion of its section which is visualated while the section on the 1500 pen is solid. We probably can't be sure why the price seems to have gone up on the seemingly same model, i.e., input cost increases, smart marketing, etc., but it does appear that prices did rise on the same model. I welcome other views on what might have been going on.
On tip of tongue I don't have emphatic answer, though I have suspicion (which itself, if wrong, will serve only to mislead), and with 1947, 1948 and 1949 catalogues on hand, I should be able to pin some of this down.
First, though it might be misdirecting, is to inquire as to whether both your pens are same era. Both are Forticel (injection plastic), but is one plunger fill and one Touchdown? At least then we would have slightly different eras in play, though a legit price bump would still be interesting.
Second, my recollection (at moment a bit vague I admit), is that while the 1945-7 celluloid full length gold-fill cap pens were found as Crest (1500) and Crest Deluxe (1750), that the Tuckies tend to pack the 1750 imprint from that era.
Your pens are later, either 1948 if plunger fill or 1949-50 if TD. If the 1945-7 Crest Tucky was 1750 coded, I would be a bit surprised to see price drop back then bump back up all within a couple years 1948-50.
Third, I'm bit surprised to see an opaque section on a Forticel pen pen. During the celluloid era the sections had become transparent. That continued through 1951 TM Touchdown, though Snork in 1952 returned to opaque sections. I'm not sure what to make of an opaque section on your pen. I'm open to ideas.
Finally, I do wonder about cap swap. Assuming I'm right that Crest Tucky had a $17.50 price by 1947 (pre injection plastic), I note that Sentinel had a $15.00 price, and that a Crest cap on Sentinel barrel (steel cap pen) if from same era would have white dot in same place, the price anomaly... and so forth.
Of course, I could be wrong and maybe there was some price hanky panky.