In one building I noticed that Elevation output from the Level Identity component is different by 10 mm when converted to numbers. I can’t share a piece of the Revit file now, but a screenshot may be enough to communicate this problem.
If you change your Level Style to report Elevations from ‘Survey Point’ conversion to string will reflect this and will say
‘Survey Point’ + 10
‘Survey Point’ + 4010
‘Survey Point’ + 510
In this case.
But no matter how the style is formatting the Elevation, Grasshopper needs a stable coordinate system and it uses the world coordinate system called ‘Internal Origin’.