Hi,
Someone asked me how to do a 'freshen' with 7z, which led me into the docs and eventually the source. I noticed that the GUI code looks like it supports Freshen & Synchronize operations, while these are missing from the command line client. You can reach them by proper application of '-u', but this requires a level of understanding far higher than necessary.
I also noticed that the command line client already has the correct action sets for Freshen & Synchronize! So this is a very simple hack job of plumbing them out to the command line as 'f' and 's' commands, respectively.
freshen.htm & synchronize.htm are modified from update.htm. I did not strongly confirm the 'Switches that can be used with this command' sections (but did remove -si -so, which didn't seem to work with any update commands including 'u'). Nor did I update the 'Commands that can be used with this switch' section of affected ../switches/$switch.htm files.
The patch was actually created and tested against p7zip 16.02. After that, I grabbed the 7-Zip 19.0 source and verified that the same patches apply at the source level. I did not try to build, much less test: I have zero copies of Windows in reach, no possibility to test it myself.
I believe this more-or-less addresses your outstanding issues:
Bug #1018 '"Broken" links in documentation'
(https://sourceforge.net/p/sevenzip/bugs/1018)
Feature request #881 'Need "Freshen" Command'
(https://sourceforge.net/p/sevenzip/feature-requests/881)
Possibly freshen.htm (and update.htm) shouldn't xref delete.htm