Young came out with their "pattern" system in 1925, which also corresponds to use of erinoid for handle grasps.
Most "lead finished" reels (arsenic acid bronzing + lampblack) were made in the '20s.
In the 30s, most Young reels were Japanned enamel (black iron-oxide baked slurry).
However, some 30s reels were still leaded - everything sent out from their wholesale catalogs used a menu for the merchant to choose options and finish.
Hard to see above, but my 3-1/8" pattern 16 is Japanned enamel, and my 3-3/8" reel is lead finished.
Easier to see the worn lead finish on the trout photo.
Here's the worn Japanned enamel on the 3-1/8" Allcocks Stockbridge.

and '39 Allcocks catalog listing
Perfect Japanned enamel on a pattern 1c Allcocks Ousel
High-remnant lead finish on pattern 8, though you can see where the top lampblack layer is wearing.
The "lead" btw, refers to the pencil graphite in the lampblack.
