Got the little Snubby recently, and promptly sent off for a Book about Ivor Johnsons, and have been reading up on them.
Pistolwise...in 1909, on through around 1911, I J revamped the whole lineup for handling 'Smokeless', electing new Alloys and Metalurgy and also re-designing pretty well everything.
As you can see, this example has a positive Cylinder Locking Lug, no behind-the-Trigger 'release'.
All in all, it is snug, smooth action, very well made, very good fit-and-finish...tight lock up and rock solid all round.
The final form of the 3rd Model, went from 1911 to 1941.