By itself, Griffith doesn't seem to have any
batch capability?.. So, anyway, you could actually
import the movies assuming your "simple office spread sheet" is in one of the formats supported - like: CSV, XML, etc.
If we're to take a CSV (comma separated value, a standard for Office Excel), you can see from a test griffith_list.csv (which can be exported -below
Import- from the
File menu) that there are these sections:
number,o_title,title,director,year,classification,country,genre,rating,runtime,studio,seen,loaned,o_site,site,trailer,plot,cast,notes,image,volumes.name,collections.name,media.name,screenplay,cameraman,barcode,color,cond,layers,region,media_num,vcodecs.name
& your own file must follow this (all sections have defining codes, to match the top order). For example, each complete entry ends with:
,,,,,,0,1,
Afterward, you could select
Fill empty fields only from the
Edit the movie details dialog, but again, only if there were some kind of a
batch function for Griffith itself (otherwise you might as well enter each movie, one by one, right?..

).
P.S.
The .CSV was opened/edited from a text editor, like
Notepad++ rather than Excel, and/or the associated program itself.