Well you're obviously accusing everyone in the new testament from being a stones throw from denying it because nobody invented a day to observe it. There's no doubt that they recognized it, but they also recognized that his atoning death at PASSOVER was the most important aspect and was the scriptural thing to be observed.
Not so. His death at Passover would not have saved anyone unless it had been followed up by His Resurrection on Sunday, the day of First Fruits.
The oft-quoted salvation verse of the NT Romans 10:9 reads:
"That if thou shalt confess with they mouth the Lord Jesus, and believe in thine heart that God raised Him from the dead, thou shalt be saved."
Salvation required belief in the Resurrection. The Resurrection was evidence that His Crucifixion on Passover had not been in vain. Observance of His Crucifixion on Passover can be done without any recognition of the Resurrection, but observance of the Resurrection is impossible without recognizing the Crucifixion that put Him in the grave to begin with.