Dressmaking Pattern Explanation

I have just bought a dressmaking pattern of a bridesmaid dress to make
for my daughter. I am in the process of buying the fabric to make it
& have come across a small problem that I would appreciate some help
with.

The part I am stuck on is the width of the fabric for the underskirt
made or tulle/net. Usually it states a width i.e. 45" then underneath
it will state 60".

i.e. 45" 3 1/2 yards
60" 2 1/2 yards
This part however states 72", 108". but the amount of fabric is the
same.

i.e. 72, 108" 4 1/2 yards

Why does it have a comma between the 2 sizes?

Also, I am struggling to find tulle/net in those widths! I can only
seem to find 54" wide. Any help please?