We have just come off the splendour (8 days ago) and was quite surprised at the dress code on both formal and informal nights. Formal nights there were mostly suits/ties/dickies but I am not sure I remember one tuxedo and some were just in shirt and tie and no jacket.
Informal nights there were even jeans in the restaurant which I for one have never seen on a cruise before.
Anyway as long as you are wearing a shirt and tie you`ll be fine.
You will find some guests wearing Tuxedos but a lot of guests will be
wearing suits and ties, the decision is yours so don't worry about a specific
dress code you will not look out of place. My next cruise will be the 70th
for me and I don't take Tuxedos any more. Enjoy.