It works quite well in my testing so far. In most cases, even with multiple sequence values, the first sequence value changes under outlining commands as one would expect it to (at least in the Outline tab view). Thanks a lot and sorry about all the extra work this led to!
I have a related suggestion, which I give hesitatingly, given all of the work you have already put in related to this feature: when I select a note in the Outline tab or in the List tab, when sorted by sequence, the App presumably knows the value of the sequence field that is used at that instance of the note. Would it be possible to have a context menu command that cyclically permutes the values of the sequence field so that the value of the sequence field that corresponds to the position of the note comes first? This would allow one to easily use all of the outlining commands with all of the sequence field values in two steps.