NFHS 6.1.2.c
the pivot foot may remain in contact with or may push off and drag away from the pitching plate prior to the front foot touching the ground, as long as the pivot foot remains in contact with the ground and within the 24-inch length.
ASA 6.3.I
(Women's and all JO play) In the act of delivering the ball, the pitcher must take one step with the non-pivot foot simultaneous with the release of the ball. The step must be forward and toward the batter within the 24-inch length of the pitcher's plate. It is not a step if the the pitcher slides the pivot foot across the pitcher's plate toward teh batter, or if the pivot foot turns or slides in order to push off from the pitcher's plate, provided contact is maintained with the plate. Raising the foot off the pitching plate and returning it to the plate creates a rocking motion and is an illegal act.
NCAA 10.4.1
In the act of delivering the pitch, the pitcher must move toward home plate by pushing off the pivot foot from the pitcher's plate, taking one step/stride forward toward home plate and landing on or within the lines of the pitcher's plate.
NAFA 9.4 - Step/Stride
In the act of delivering the ball, the pitcher must push off with the pivot/drag foot from the pitcher's plate and take one step/stride forward toward the batter, on or within the 24-inch length of the pitcher's plate.
So, what I'm reading is that the codes agree with the exception of the NFHS which requires the pivot foot to remain within the 24-inch length of the pitcher's plate. The other three codes only require the stride foot to remain on or within the 24-inch length of the pitcher's plate.
Additionally, just because an umpire didn't call a pitch illegal doesn't necessarily mean it was legal and conversely, just because an umpire called a pitch illegal doesn't mean it was. It is like a strike call - you are at the mercy of the umpire and what they 'perceive' the act to be, legal or illegal. And if the umpire doesn't understand the rule or the differences between the codes, you are going to have issues.
The true measure of the pitcher is how she adjusts to what the umpire is allowing her to do.Last weekend I was in Glen Ellyn, IL working a tournament and BOTH pitchers completely buried the pitcher's plate every half inning. I could not see if either of them were in contact with the plate. One coach decided to 'inform' me that the opposing pitcher was not in contact with the plate on the back side. I informed him that I could only call what I could see and since ASA doesn't have a penalty for covering the pitcher's plate I could not see if she was in contact or not. When she didn't completely cover the plate, I could see she was in contact.