I even freeze and refreeze store bought box stocks.
I also freeze unopened boxes when they get out of date. They will bulge a little, but there is enough room in the box to freeze it still sealed.
If I use a partial box I put it in the freezer. More than once if necessary.
We make homemade stock too and freeze like you do. If there is any left, back into the freezer it goes. My store bought stock is here for one reason only. Just in case I'm out of homemade.
Now, I will never try to make beef stock again. Its much easier and its also somewhat inexpensive to buy it in a box. And its pretty good. I don't ever buy canned stocks and really don't know why. I just don't.