Leadership Theories (Syllabus Section D1d)

Good Day,

I am having trouble understanding the different leadership theories. I have several different resources that I am using for study (ACCA-X, OpenTuition, Kaplan and BPP) from several different years (2015-2020). The problem is that they refer to different names for the theories and list the corresponding writers under these theories. Here are some examples:

Kaplan Pocket Notes 2015
– Transformational Theories, Bennis and Heifetz
– Behavioural Theories, Blake and Mouton and Ashridge
– Contingency Theories, Fiedler and Adair

ACCA-X Course 2020
– Trait Theory
– Functional Theory, Adair
– Situational Theory,
– Contingency Theory, Fiedler
– Transformational Theories
– Style Theories, Blake and Mouton and the Ashridge school

BPP Interactive Text 2017
– Train Theories
– Style Theories, Blake and Mouton and the Ashridge school
– Contingency Theories, Fiedler, Adair, Bennis and Heifetz

I am confused with the contingency theories and their writers, they seem to overlap and I am not sure as to which theory they each belong. Are these changes caused by the syllabus changing or am I missing something?

Thank you for any help, Christy