NT scan, usually done around 11 to 13 weeks, and the quadruple test, done later around 15 to 20 weeks, screen for different things, so one doesn't normally replace the other unless your doctor has a specific reason.
Next Steps
Ask your doctor directly whether the NT scan was intentionally skipped or simply not scheduled yet, since it's still worth doing if you're within the window.
Health Tips
Don't assume it's been covered without confirming, as this scan has a narrow time window.