Hi,
ZyGrib is still running, but no update have been done since 2016. XyGrib has some new functions that many of us wanted to have.
To have all the signification of variables used by NOAA is their grib files, you'll find them on their websites (I know it is not very easy to find things on their websites)
In the example you gave, CRAIN is the cumulative precipitation, and it possible that this name is not yet recognised by XyGrib.
Grib2 is a format, but their is no complete standardisatioin of the content (including names of variables).