Some 42 inch fabrics have been around for at least 20 years.
One just needs to CHECK the width and not assume any particular dimension.
If one is a washer, one needs to factor in that SOME fabrics shrink widthwise instead of lengthwise.
Some fabrics don't shrink at all - a very few seem to "spread out" - some shrink only in one direction - some shrink in both.
I can't tell by looking at a piece what it might do.