I think we're mixing up terms and funtions here some. The selector toggle on the hammer allows you to select either the centerfire firing pin or the rimfire firing pin. When the toggle is in the center, it acts as a safety by not allowing the hammer to hit either of the two firing pins.
On early Contender frames, you were required to cock the hammer and use a screw driver to turn a selector on the face of the hammer 180 degrees to select either the centerfire firing pin or the rimfire firing pin. Sometimes in the mid '70's, T/C added the slide bar to the hammer, which acted as a safety. Firing pin selection was still as before, using a screwdriver. If the slide bar was pushed to the left, it would push a small pin out from the hammer, which would prevent the hammer from hitting which ever of the firing pins that was selected. Problem was, if you dropped the hammer with the safety engaged a few times, it would tend to jam the slide bar. Sometime in the later part of the '80's, T/C did away with the rotating firing pin selector/slide bar hammer and went to the toggle firing pin selector switch.
In 1988, T/C & IHMSA did a 10th Anniversary edition Contender in 7mm TCU. I have one of those and it has the slide bar safety hammer. A years or so later, T/C & IHMSA offered a matching serial number 10th Anniversary Contender in the 7mm SuperMag. The one I have of it has the toggle switch hammer. So the toggle came into use somewhere around 1988 to 1990 time frame.