1902 Enlisted Bell Cap Branch Insignia dates

[Redleg]

What date was the 1902 Enlisted Bell Cap insignias replaced by the eagle on disk cap device?  I have collected a few of Artillery cap devices as shown here.  Is the branch insignia, without a regiment, earlier than those with a regiment?   (The plain artillery device had some verdigris on it.)  

[CAC1901]

The eagle disc is in the 1917 Uniform regs, replacing the branch of service device. Artillery enlistedmen, whether field artillery or coast artillery, wore cannons with their unit number. When field artillery went back to the regiment/battery organization iirc in 1907, they used the number & letter again - the one on the right.  When units were renumbered or soldiers transferred, it was not uncommon for them to break off the 'old' numbers until they would get a new unit designated device. Like the one on the left