The area that says to mount the TV may contain a piece of plywood mounted between the studs in the wall. Using an ultrasonic stud finder and pressing against the panelling should be able to help determine if it is a piece of plywood already mounted inside the wall. If so you might not need to use a mounting board.
If it is an interior wall you are mounting to you might be able to do what I did. Provided the 2 of your 3 horizontal holes are not too far apart.
My interior walls are about 1 inch to 1-1/8" thick. This includes the "stud" and both pieces of panelling on each side of the wall. Using an ultrasonic stud finder I was able to determine that the "studs" varied in width from around 1-1/2" wide to 2-1/2" wide. They are basically 1x2's and 1x3's.
The locations for the tvs had folding shelves for both tvs. The brackets for the shelves were mounted to pieces of plywood located inside the walls and fastened between the wall studs. I lowered the dining area tv shelf 2 inches and mounted the tv swivel mount above the shelf using a wall 2-1/2" wide wall stud. This left room to stack the satellite receiver and a DVD player on the shelf.
My swivel mounts had 2 vertical holes large enough for 1/4 inch fasteners. I used the mounts as templates and drilled through 2 of the 1x3's and used 1/4" bolts, lock nuts and fender washers. The nuts and fender washers are on the opposite side of the wall and can be seen, but it works for me.