I found some more info. Although the One SL has not had a ‘generation’ change it seems there were some (presumably) minor changes to it. Another user here in the community mentions this…
There are three versions of the One SL: S22, S38 and S43, the model # should be on the base. S43 is new and is S2 (Sonos App)-only.
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Although the early One SL was available for a Sonos S1 system, once it had been updated to an S2/Sonos App System setup, there is apparently no way to return it to an S1 setup.
Hope that information assists here too.