I've just brought https://wiki.koha-community.org/wiki/Customising_Notices_and_Slips#Notice_Specific_Markup up to date with master. The 'Can be branch specific' column is no longer needed; as far as I know, any notice may be branch specific at this point. The only gap on the wiki are the letter codes for notices generated via SendAlerts -- If someone can help me out there, that would be great.
Notices and slips documentation has been completely rewritten, bug now irrelevant https://koha-community.org/manual//24.11/en/html/tools.html#notices-and-slips