Someone here on the Dis suggested that when you customize your Magic Bands, you include the date (or at least the year) of the trip. This makes it really easy to tell how old a Magic Band is. Before I saw that suggestion, I would use my initials, and that made it hard to figure out how old they were.
I just went through my Magic Bands and separated out the older ones. (I have three from 2017; my older ones are from 2015 and earlier.) I pulled off the grey part and started making a Magic Band Chain. I'll probably put it on my Christmas tree when it's longer. I de-activated these old Magic Bands in My Disney Experience. When you are having a Magic Band problem, sometimes a cast member will tell you that the problem is caused by having too many active Magic Bands. While this may or may not be true, there's no reason to have the older ones active when I know I will not be taking them with me.