justsaymaybe
This example works here:
So I create a 4 bar clip, then ctrl-drag to the right in the MIDI track (to bars 4-8), then right-click "unlink step sequencer clips".
The next pattern I load in step sequencer overwrites bars 1-4, but 4-8 is untouched. I can repeat with the new clip, and so on ...
Yep, that is basically what I am doing as well. It is weird that you have to move the clip ahead as it always overwrites the first one. Even more confusing when you have clips of different lengths. I am powering through it but I am surprised they didn't make this easier and more logical.
Another method is to drag the clips into cells in the matrix view to organize them, but still need to unlink them there, or the pattern will be replaced when you load a new one in step sequencer.