Quite some time ago I raised an issue found whilst planning in PFPX where a number of bidirectional airways have a split flightlevel availability. The NG data supplied incorrectly limits the airway to the lower level in both directions.
Since then NG has changed its chart offering with the enroute charts seemingly driven by the same data and exhibiting the same limitation.
If the Jeppesen data does not provide for the level differences might it not be a better option to use the maximum level available on the airway segment?
The image here from UK AIP airway L60, the NG data limiting L60 to FL230 in both directions.