I knew of the deal, but never mentioned it. My share group was on older retention plans from ~2016, (55$ premium tab additional line) and I moved my main line to the $85, shared 10GB plan. It caused the rest of the lines to jump from 55 to 75, and asked if there was any way they could compensate for the difference. They said they could apply a 25% discount for two years, which is what I have. It applies to the entire account, hence the $52.50 10GB non shared plan I’m on.
Hope that helped.