This is because unlike later systems, 6-ET was not self-lapping. When the EQ reduced to the proper level he would place the valve back into Lap. In order to make a brake pipe reduction the engineer would put the valve into Service and carefully watch the Equalizing Reservoir (EQ) pressure. Release was followed by Running (kept the brake line fully charged based on the EQ reservoir), Holding (released the train brakes, but kept the engine/tender brakes set), Lap (more on that in a moment), Service, and Emergency. Kind of a "cheat" (similar to F7) you had to be carefull not to overcharge the brake line beyond the current "normal" setting (similar to the 90 psi / 110 psi settings we use today).
The automatic positions were: Release (this opened the brake line directly to the main reservoir). The 6-ET was introduced in 1906 and became the standard brake system on steam locomotives for many years. By that, I mean that as you move both the automatic and independent valves further into the Service Zone, pressure will reduce (or increase in the case of the independent) in relation to the movement of the handle. The important thing to remember about 26-L and its successors it that they are all self-lapping. To "bail off" the locomotive brakes, the handle is depressed. The independent brake has Release and an Application Zone, where locomotive brake cylinder pressure is proportional to the position of the brake valve handle. The automatic valve features (from left to right) Release, Minimum Reduction (that initial 6psi reduction), Service Zone (the further right you go, the more reduction you get), Suppression (recovery after a "penalty application"), Continuous Service (leave it long enough and pressure will go to 0), and Emergency. The operation of the brake valves currently in Run8 are based on the Westinghouse 26-L system which was introduced in 1957.