Current extension repositories have REL1_23 branch, but it was created when REL1_22 was created too, so basically it's outdated.
They have REL1_23 updated as of 22-10-2013
I've only found one exception, though:
One particular change introduced on 1.23 release was the migration from PHP to JSON files for i18n. I think all the extensions were migrated to JSON files in master, but REL1_23 still doesn't have that change.