Latest Code =
HASONEVALUE ( Projects[Project] ),
SELECTEDVALUE ( Projects[CODE] ),
LASTDATE ( Projects[Revision Date] ),
LASTNONBLANK ( Projects[Revision Number], 0 )
The key part of the measure is GENERATE ( ... ), which finds the maximum Revision Date using LASTDATE (returning a 1x1 a table), and then finds the maximum Revision Number in the context of that date filter using LASTNONBLANK (also returning a 1x1 table). These become a combined filter, and the single value of CODE is returned with this filter applied.
The measure is also restricted to return blank unless a single Project is visible in the filter context.