I have a "shared add-in" written in c#, for which I have a COM shim
for. I've only just noticed that, whether or not it is 'shimmed', it
does not feature in the add-in manager's (tools-add-ins...) list of
checkboxed items.

It does not make a difference if the add-in is installed for 'just me'
or 'everyone' - it does not appear.

Is this list for some other type of add-in (the '*.xla' add-ins [what
are they anyway]?) or have I overlooked some obvious step?