Hi all. I have a question for the pioneers of musical theory. What are the chord substitutions did Mark Knopfler use to make the prograssion of 'Private Investigation'? The chords of the song are:

Em, Bm, Bm, A
G, F, B7, Em
Edim, Am6, B7, Em


(they will be familiar to those who know the song).

I know the common chord substitution rules, but they couldn't explain the chord changes for me.
Thanks in advance.....

Sherif