@sallyhinch, that can be a problem.
You want an inner tube that has the same number on it as the tyre. It can fall within the range so if you have a tube that goes 700 X 18-25 it obviously works on a tyre that is 23 or 25 (never seen a tyre that is 18)
And
If you have a tyre that is 700x 25-35 it will fit a tyre that is 25 or 28
However what would be useful but ypu do not get is 700 X 23-28
Or maybe you do if you look hard enough?