z/VM 5.2 install

[Steve Gentry]

Hello.   I just received zVM 5.2 on DVD.  I'm looking over the summary sheet for  a zVM 5.2  DVD installation and it looks like I've got a problem.  I will be installing this 2nd level and according to the summary sheet my first level machine must zVM 5.1.0 or higher.  Is this for real?  Why can't I do a 2nd level install on zVM 4.3?
And I also received a zVM Stacked Recommended Service Upgrade 5101 dvd.   There is also a zVM Stacked Recommended Service Upgrade 5201 dvd
Why was the 5101 shipped?
Thanks,
Steve