Luminance coefficients used throughout the engine not matching sRGB standard

This is causing confusion when working with color in UE5, specifically when validating for HDR between different reference materials.
It has also been noted that the color primaries in PAL and NTSC have many values that differ from sRGB primaries.

Compare and review sRGB luminance coefficient value calculations used in the engine for discrepancies and differences to each other.
There appears to be differing variants of these values for what should be standardized across the board.
As an example: Luma() in LumenReflections.usf and GetLuminance() in Color.h have different values.