It is indeed how virtually any program works. Once you hit a level, you need to requalify within (usually) a year by gaining status miles again (sometimes with the same amount, sometimes with a lower amount as for first qualification). That you have a rollover (albeit of 5 XP only) may not even happen in other programs. The main difference with other programs is that with FB you first qualify for silver, are then going to 0, and if you want to go to gold, you need to gain the full 180 XP again. With TK fi it may be if after T=0 you hit 40k in one year or less you become Elite, but if you score another 40k in the year after T=0 you have 80k in total qualifying for Elite plus.