Pathfinder 1E Planar Ally Table HD Limit

[Laptopdude]

I've been puzzling over this for quite some time now, namely the fact that Greater Planar Ally allows for up to 18HD of creatures, and yet if you visit the d20pfsrd page, the table goes up to 22HD.

The only thing I've managed to find is a 3rd part feat, Planar Caller, that lets you add +1HD to the creatures you summon via Planar Ally.

Was this just a mistake or is there actually a reason for it?

Thanks,
Laptopdude

 

[Cadence]

I was trying to find a feat or something that raised the allowable level... but only found one for 3/3.5 so far.