I'm unfortunately not there physically to help, but my mom has this light switch she needs to remove temporarily and replace the plate. Her "handyman" installed it 'brand new' within the past few years. I told her it looked like it was from the 80s haha. Anyways, she apparently cannot remove the knob for the life of her, shouldn't the knob be able to simply pull off without breaking?
Yea you are right, I would say 1990s based on the wattage rating being on a metal plate embedded into that plastic. Not newer than 2000 unless it is some very specialty company.
Yea all of them should be able to pull off because the cover cannot go on with the knob on there. However there could be a screw in the side holding it on, can't see all the way around it. If your mom is old she might just have shit grip strength and can't grab it to pull it off. I know plenty of older women that have what I'd consider no strength there at all, that is all forearm.