Take my word for it,.. "Baggage handlers" are not stealing your bag tags. Do you have any idea how many bags a baggage handler sees/touches a day, they don't want any souvenirs.. I don't care how "cool" your bag tag is, it bears NO novelty to a baggage handler..
It's much more likely that the tag simply came off at some point. If you think anything is too sturdy to be ripped from your bag, you must have NO IDEA what happens to your bags once they disappear behind the little hole in the wall..
I could probably come home with a grocery bag full of bag tags every day just from the ones I can pick up off of the floor and out of the bottom of baggage carts..