Not sure how that works, but don't Clarke and Bueckers have the option of a covid year...and Bueckers just missed an entire season. So all 3 could potentially end up in the same draft....I think.
The extra year option is potentially giving a few top draft prospects some say in where they wind up. They have a little extra leverage in the process. For example, suppose Boston didn't like the prospect of playing for Indiana (certainly not an inconceivable thought). She could tell Indiana if you draft me I am going to play another year at South Carolina. If you trade the pick to a team I don't like, I won't play for them that first year either.
Now I presume the team that drafts her would retain her rights beyond the first year, but my point is that extra year gives a few players leverage that they didn't have previously. In addition players have the European option where they can make as much or more than they can in the WNBA anyway, so they could avoid the league all together if they really wanted to.
This offseason has seen a player (JJ) say they wanted out, and then be traded for what appears to be far less than fair value. This is happening more and more, so the idea that a team has solid rights to a player for the length of the contract is not what it used to be either.
Anyway players at the top of the WNBA draft are in a different position than they have ever been before. We also previously had only a few players each year that had to decide whether to declare for the draft. Those were players old enough that they could declare after their junior year, but there were only a few in that position. Now everyone who played during the year without a championship has that option and can compare or project where they might wind up this year vs. next year for example.