Thats a crazy number of instructors. I had a similar situation when learning to fly gliders, with a non-profit club and volunteer instructors I took what felt like far too long to get to solo because of having a different instructor each day. I knew I was good enough but the instructor of the day didn't because he didn't know me.
After a break of several years from flying I went and bought a flexwing and started taking lessons at a microlight school. I camped on the airfield each weekend and was one of only three students. My instructor remained the same and I soloed in under 5 hours. 2 of those hours were spent un-learning the urge to 'pull-back' to go up thing. This validated my feeling that I was competent and just needed a consistent teacher to bring on my training.
I then had another big break from flying and came back to it a couple of years ago and took 9 hours to solo so I guess either I'm getting worse or the official syllabus is now being more rigidly applied.