Seven years of full time instructing and no other failures? Either:
A) Examiners are lenient
B) You need more students ($)
C) You're a great instructor! Your shame is a byproduct of prevailing notions of perfection at your flight school!

343 students trained in 7 years. Been doing this in South Carolina, Colorado, South Dakota, and Pennsylvania with several different examiners. Just always took the advise of the examiner who did my CFI ride. "Don't train students to just pass a checkride. It leaves to much wiggle room for failure. Don't waste their money but train them to be a pilot."

What kind of training were you doing? I started training at a small college with a 141 program and had a perfect pass rate, went to a bigger school in Florida with foreign students and that changed in a hurry...

"Ah sir its ok if I unsat we just go fly more"

Done just about all. Small part 141. A C150 and me part 61. A college part 141 now.