@vapilot
One would assume that since thrust commands (TLA or A/T) and actual thrust levels (EPR/N1) are key data points that the resolvers should provide the data for the manual thrust command FDR traces.
One should always be very careful as to what one ASSUMES about FDR parameters.
As you say, you'd think that something like TLA would be a fundamental FDR-required parameter. But it isn't! Part 121, Appendix M only requires that "Throttle/power Lever position" be recorded "For airplanes with non-mechanically linked cockpit engine controls". (Item #42 in the table of parameters). So for aircraft like the accident aircraft here, which is a FADEC engined aircraft, TLA is required. For any hydro-mech controlled engine, there's no requirement to measure TLA (or equivalent) AT ALL.