adding another layer of subfloor

so I had to use floor leveler in one room before laying hardwoods. So now the adjoining room needs to have subfloor raised before laying hardwoods. the original subfloor is advantech 3/4 tongue and groove and I am putting another layer on top of it. Now the room is just under 16' so two sheets would cover it, but when original subfloor was laid, before walls, the room was obviously larger than 16' so the end of one row has a piece that is about 3" (with another 4 1/2" under the wall) if I lay 2nd layer over 1st, using opposite spacing of joints, I will come up a little short. hard to explain but typically on one row you have joint then next row you normally would place the joint at middle of a full sheet from previous row-staggering the joints by 4'. any issue with staggering this a few inches? that way I could use two sheets for the span. otherwise, if I center the joint in the center of the previous sheet, I will end up with 3 pieces total with one piece only being about 3 inches. also, what is spacing to use to screw the 2nd layer to 1st? every 8"?