It appears that the March 23rd date, was a rumor to help track down some leakers. However, evidence is pointing towards an even sooner rather than later. At present, several devices are showing on Amazon as not being in stock until April 7, and a MacRumors member found a case for a iPad Pro (2021), for sale at a Target, that wasn’t supposed to be on the shelves until April 6.
This leads me to believe that we will getting our even still. It will likely be April 6th, with new iPads available either later that day, or on April 7. There is a small possibility that the event will be March 30th, but for that to be the case, invitations would go out on the 22nd, 23rd, or 24th. We’ll all soon find out.