[4] Power reverse gear was fitted slowly to the entire class per an order of the Interstate Commerce Commission, the task being complete by the early 1930s.

Fitting this gear required moving the air tanks from the right-hand side of the boiler to the front deck, thus providing an easy visual indication of the modification.

[4] Most (but by no means all) of the class were eventually fitted with mechanical stokers; by 1947, 512 locomotives were stoker-equipped, 39 still hand-fired, and the remaining ten were oil-fired, the latter being an experiment tried during the coal-miners' strikes of that period.

[4] Many of the class were fitted with cab signal equipment, the electronics for which were largely contained in a wood box affixed to the right-hand side running board in front of the reversing gear and aft of the smokebox.

[1] L1s #520, which remained in service until almost the end of steam operations, hauled one of the last steam-powered passenger trains on the PRR: a railfan special between Enola Yard and Northumberland, Pennsylvania.

In HO scale, hundreds of hand-made brass models of the L1s were supplied from 1965 to 1976 by United (Pacific Fast Mail), and also by Key Imports in 1978.