This is April, and everyone is waiting for April security patch, not for March. Well, Unlocked Galaxy S9 users in Germany receiving mew software update, and this update brings latest April 2018 security patch.
The Galaxy S9 Plus users still waiting for this update. We have verified that the April patch is only rolling out to Galaxy S9, but the S9 Plus users will get it soon.
The update is rolling out as part of software version G960FXXS1ARD1 for the Galaxy S9. This update is small in size, 61MB. You can try a manual update via the Settings > About phone menu.
Image credit to Sammobile