After discussion with CaptainSandL ... thread re-opened and back to the top. Following is from the second post (Terraplaneblues) in the Flight Test thread ......
Boeing Service Letter 737–SL–27–069–A explains it all.
Here is the gist of it.
-100 -200 aluminium structure elevators & tabs
Classics have composite elevators & tabs - titanium tab rods are better thermally matched to the composite elevator tab structure - results in less tab trailing edge deflection due to variations in temp. (than an aluminium rod set) so the limits were increased as a result.
The other factor classic to NG is mach trim compensation differs for aerodynamic reasons, reflected in type of FCC.
The -600 -700 -800 tolerances are not all the same as each other in the AMM.
Hope this helps