Compare like with like
Enter the pattern amount and, when known, the usable WOF it assumes. A different current usable width makes the comparison informative but not directly like-for-like.
Keep stock out of the comparison
Pattern yardage describes a fresh purchase scenario. Fabric already owned may reduce what you need to buy now, but it must not reduce the fresh comparison basis to zero.
A difference is not an error verdict
Construction method, trimming, shrinkage, squaring, miscuts, fussy cutting, direction, and designer preference can justify allowances. Use the project planner to see the fresh comparison and stock-aware shortfall separately.