Actually, this is an interesting topic, because there are court decisions on this in Germany.
So if an ISP has, say, a 25mbps, 50mbps, and 75mbps plan, the 50mbps plan has to provide 25 or more, and the 75mbps plan has to provide 50mbps or more.
I decided last year that I want to move to Germany within 5 years. (For various reasons) Since I've made that decision, I keep finding more reasons to do so.
So if an ISP has, say, a 25mbps, 50mbps, and 75mbps plan, the 50mbps plan has to provide 25 or more, and the 75mbps plan has to provide 50mbps or more.