There is a very SUBTLE POINT about changing instructors and it has to do with COMMUNICATIONS.
I have actually witnessed incidents caused by the Instructor (new) assuming that the student already has certain moves mastered.
If I take on a beginner for instruction, as we move ahead I learn what strong points and where the weak points are. This works like a data base.
There are certain students that move away and show apparent proficiency in flight. The new instructor then somewhat relaxes and gets hit by the unsuspected "weakness"....this could be anything, turning right turns, or no perception of approaching stall, etc.
My preference is to keep the student from start to finish.
Nowadays this is becoming more and more do-able since the newbies show up with a bunch of
simulator time behind them which reduces the training time considerably.
I was actually able to graduate a 25year old rank beginner in about 4 hours (one day) TOTAL