That seating issue happened to us a bit back and I called Swiss air and gave them my Delta confirm number and they gave me the Swiss confirm for the Swiss Air segment. I could then log into Swiss Air and choose my seats....this was three years ago so I don't know if it still applies but worth a call.

..and..RE: Delta Comfort+....interesting. I checked the Delta website for a SXM-BOS return on 1/26 and it only had "main cabin" listed as a possibility...one column....no "sold out's"....but we are in Comfort+ on the flight I checked so they must only show availability...and...I love the Comfort+ seats but I have noticed as they fill up the price increases ....but, with that said, the starting price is higher than it used to be ....