There is also one more case

Between 101XP and 179XP = you will be deducted of 100XP, will be silver for one more year and the leftover will be kept for the next year

So you need to plan everything correctly , if possible of course

it can be worthy to do extra steps if , before the end of your 12 months period as silver , you get close to 180XP , so you can reach gold

On the other hand , if silver is enough and you go over 100XP just a bit , then these xp left will count for your next 12 months period