Go TabGroupList deletes the tabs already present

The command Go TabGroupLoad MyTabGroup TabCloseAll=No adds the tabs in MyTabGroup, without deleting the tabs that are already present. But the command Go TabGroupList is not modified by TabCloseAll=No — the tabs already present are deleted.

How do I select a tabgroup from the tabgroup list and add the tabs to those already present?

If you look in the preferences, under "tab groups", there is a checkbox for that in the settings of each entry ("close all open listers").
If you uncheck the one in question, it should work.

I meant "close all open tabs", of course. Sorry.

Thanks very much, abr. It's all sorted now . . . and I am feeling a little silly, because I had read about this checkbox, but then forgotten about it.