And can V9990 only be found in addon GFX cartridges?
AFAIK, yes. The Turbo-R uses the same V9958 that MSX2+ machines have, IMHO it's basically an MSX2+ with a fast 2nd CPU (R800) tacked onto it. And some minor improvements like built-in DOS2, system timer, MIDI for the GT, and more RAM than usual for Japanese machines. Which is why this machine has always been too expensive for the hardware it offered (talking about price here, not about the value it might have to its owners... 
).
Well, it should have had the V9978, with full backward compatibility, to be more exact 
I have used the manual and still use the manual on a regular basis having learned most of my VDP skills from it. Therefore I propably have beta tested it quite well. Because of this I have been able to find some minor and major errors which I will point out per page:
page 3, The V9990 has not been used in the Turbo-R (Everyone allready commented that though)
page 11, At VRAM, the tekst says "Vide Random Access Memory" should be "Video Random Access Memory"
page 13, Port description table is missing the ports functions.
page 14, at the Register 17 table, Auto increment function is described wrong. 0 enables auto increment, 1 disables it
page 16, at step2, Table says register 45. Should be register 14
page 69 and 85, register 36 and 37 table. All capital D's should be a capital S.
page 71 and 81, register 36 table right description. Source should be Destination
page 78, register 32 up to 35 tables + description. All capital S's should be capital D.
There. I really hope to have helped finding the mistakes. Looking forward for the V9958 Manual 
