Confirmed upgrade M -> Z on SK907 OSL-EWR tomorrow, August 23rd. Received new e-ticket from SK in the mail this morning. ^
Still listed as "pending" on OT website though - but more the norm that I first get the upgraded e-ticket and a couple of hours later the notification from Optiontown.
(Last time I actually did not get the upgrade notification from either SK or OT until landing in CPH, but received a nice surprise when checking into the flight at LAX and receiving a Z ticket on the ORD-CPH leg).
Success rate 4/5 so far since October. Three in Z and one in Y. Happy flying everybody!