What fhqwhgads said.
If you need a patch 2 boards wide, lay in the first piece whole. Cut only the lower half of the Groove off the second one. This way the top will still be supported by the tongue of the next board in the floor and it won't see-saw.
Also use a good glue on the ends and joints of the patch boards and it will be bomb proof.
I have included a quick paintbrush drawing of what I mean.
