It's simple,
H24 & HR24 + SWM Head = No BBCs
H24 & HR24 + Non-SWM Head = BBCs
H23 & HR23 = No BBCs Ever
H21, HR21 & newer + Non-SWM Head = BBCs
H21, HR21 & newer + SWM Head = No BBCs
( Not that I don't think any recievers before the x21 series support SWM - So you're SOL if you have a SWM dish )