You could make a comparison with your existing shafts.
Put two nails in a board about 26" from each other.
Screw that board to a wall.
Use a 2# weight of some sort and hook it onto the middle of your arrow.
Mark on the board the top of where that arrow bends to. Be sure to mark the spot accurately with a straight edge held perpendicular to the board, and make a note of the spine of each arrow.
Repeat with several different spine arrows.
Finally, put in those old shafts. You should see very clearly where they fall on the spectrum.
You don't really need to use 26" and a 2# weight. Actually using 28" and the 2# weight will give you a larger gap between the different spines and is easier to read.
The reason for doing this is to make sure you don't shoot too light a spine in your bow. I did that once and had an arrow shatter on me.