They will be there .. Dutch government finished all the burocratic hupla. I think the biggest issue is basing the planes in Ukraine. I'll expect some to be stationed in the EU and Ukraine rotating them out for big maintenance. And keeping it in the news is a part of the media strategy too.
It's basically impossible to keep something like this a secret. The pilots have been in training a long time and they're not just sending planes, but also the means to maintain them.
Besides there are dangers in keeping it secret. Having F-16s suddenly doing attack runs on the Russian military out of nowhere could result in the Kremlin coming to the wrong conclusions.
Why do you believe they won't do combat missions this year? I have no perspective on this so truly a genuine question. I know there has been training for a bit now, so I figured that would make pilots combat ready and I assumed they're already have been planning for the arrival to be ready.
I think it would be wise to wait until they have the initiative again so they can combine all efforts with greater effect and safety. Ukraine's last offensive was a wash because of the fortified line and mines which slowed them down enough to be easy pickings for Russian air attacks.