Since no one else has asked this it may be a stupid question, but why are the dates of April 14 and April 26 listed, as there is no “event” listed with them?
It's actually a good question. From the past this is generally like this:
Those two dates are more likely regular practices with several controlled scrimmage segments and aspects built into them. They might have 1 vs 1s or 1s vs 2s in scenarios like goal line situation, 3rd and long, 3rd and short, or 2 minute drill. Chains never move. Pretty controlled on down and distances. More intense than a normal practice, usually a week out from a major scrimmage. Could be to thud or to the ground live.
The 9th and 21st is straight up scrimmages 1 vs 1s, 2 vs 2s, 3 vs 3s, 4 vs 4s, no other practice segments. They'll start on first down at a certain yard line and move chains on 1 downs. On 4th down or score they'll bring in the next group and reset until score or 4th down. Usually to the ground live except QBs.