Discrepancy ought to be rather less than that.
Generally, the main bits which give problems are associated with
(a) centroid approximation for a loading area
(b) figuring variable things such as occupant movement in flight
(c) linearising fuel arms
and then the error analysis (which ought to be, but is not always, done) which may fudge the sheet CG limits to make the completion conservative.
For spreadsheets, if they are to be used by others, the main concern is protecting against third party errors in use compromising the calculated results.
By all means send me a copy and I'll have a looksee.