I am a little (Time zone) late jumping in.
SGC #
are per file (as you discovered) and are defined in between the <style> tags in the file <head>
SGC # are assigned
in order of usage need (Thus the seeming randomness of assignments)
A little tedious way to unify/walk styles into a (Book) single stylesheet
Copy the first files <styles> section contents to a new stylesheet (
start with the file with the most SGC's defined)
Rename the style names from SGC # to something 'meaningful' (leave the old SGC# in comments /* SGC_3 */ as a reminder)
Then Replace all the old SGC #
in the book file with their new names
Using the same NEW STYLE name, locate other book files that have a
EXACT matching
definition and ALSO change their defined name (remember to use : 'current file' in replace) to the new name .
(
let the replace change the name inside the <style> as well. When there are no more SGC's in that <style>, it can be deleted)
Add another files <style> to the main stylesheet (remove any of the the new name definitions that appear before the copy)
repeat the copy-renaming sequence until done
Once you get on a roll, it will probably take less than 30 minutes
remember to
link your new stylesheet to the files
WARNING: If any SGC # are greater than 9, do those FIRST (Extra care is needed not to change SGC-1n's along with SGC-1)