The number of rows used for business on Swiss single aisle aircraft is varied according to need, usually from a minimum of 3 to a maximum of about 10 or 12.
When more business rows are required, the economy section has to be moved back. Preferred seats are just the first 4 or 5 rows of Y.
From what I've seen, the whole Y seating plan seems to be moved back as a block.
Somewhere in the T's & C's Swiss say that the type of seat paid for, ie. aisle, centre or window is maintained, just the row number changed.