The DL18s (ILW rsx51/630s) were purchased to replace the last of the D&Hs U33Cs. The original plan was to purchase a lot more of them, but then the Chicago & Northwestern started retiring their fleet of ex-N&W C-628s and the bulk of the order became a (much cheaper) remanufacture of those well-travelled centuries, making these units the only 51/630s purchased by the PV&T.
As of 2023, all four of them were still running on D&H west (the D&H/OSW/I&M line from Owego to Chicago.)