I thought it would be of interest to take all the CD 127 W. Brookfield's with April dates and draw generalizations on the mould styles. Basically, I conclude that there are three very distinct mould styles which I've called "knob" dome, "mushroom" dome with lower wire groove lip, and the standard "mushroom" dome style with no lower wire groove lip. The insulator on the left is the "knob" dome in blue-green and is embossed "W. Brookfield 55 Fulton St" on the front and "Pat April 4 1871" on the back dome. Note - that, if you have a "knob" dome, it could be either an April 1871 or April 1870 date. You will need to check. The insulator in the middle is the aqua "mushroom" dome with a lip on the lower wire groove and is embossed " W. Brookfield 55 Fulton St" on the front dome and "PATd Apl 4 1871" on the back dome. As far as I know, only the April 1871 date can be found with a lip on the lower wire groove. The insulator on the right is a deep blue "mushroom" dome style with no lip on the lower wire groove. This CD 127 is embossed "W. Brookfield 55 Fulton St" on the front dome and "Cauvets Pat Apl 4 1870" on the back dome. Based on my experience, only the April 4 1870 dated units will have "mushroom" domes with no lip. In addition, only the April 4 1870 CD 127 carry the embossing "Cauvets Pat". If anyone else can add to my understanding, it would be welcomed.