I've got two like that. It seems that proto kept a handful of items as pebble finish for a few years (line wrenches, the larger ratchets, pickle forks, even the combo wrenches kept the small pebbled field for a while).
One thing that always confused me was the fact that I own a proto/plomb dual marked ratchet that is the standard pearhead style... so it should be earlier than any ratchet marked just proto... but then I have a proto one with the pebble finish (but no mention of Plomb) that has the what would seemingly be earlier pebbled style.
Either way - it's an excellent quality ratchet and your's appears to be in great shape. Keep it, use it, and love it!