Kjay,I read this, as long as you have met the SABC req. in 210.11(c)(1),210.52(A)(1) & 210.52(B)(1).
Your good to go,add as many switched rec. as you want on a general purpose ckt.

-IF you are counting that receptacle as one required by spacing, then you can switch only one half of that duplex receptacle. -

Where is this? I've looked.A switched receptacle is still a receptacle.
However 210.11(C)(1) & 210.52(A)(1) have to be met first.So I don't see where spacing would come into play.
210.70(A)(1) deals solely with 'Lighting outlets'.