Principles

Your tai chi lessons are about tai chi, not the teacher; the teacher must never become more important than the subject.
 Follow the tai chi, not the teacher.
 Every instructor changes what they learn, either subtly or greatly.

 This can be through a lack of understanding, inaccurate practice, or a deliberate alteration intended to emphasise one aspect of the tai chi; such as health.

 Lineage cannot prevent this change - each person adds or removes something from the tai chi.
 Every school has its own version (or interpretation) of somebody else's version...

 What really matters is whether or not your school encourages you to explore the system for yourself and whether or not it teaches the tai chi principles correctly.
 Without the fundamental principles, tai chi is not actually tai chi - irrespective of who taught who.