The OG 12 is a slightly improved version of OG 11. In other words, there is a considerable amount of overlap. However, the OG 12 has newer questions and a higher concentration of more difficult problems.
If you're using the newest edition for Manhattan, it's probably best to combine it with the OG 12. The Manhattan guides list a number of questions from the OG 12, and those numbers might not match with the OG 11. But since you already have the OG 11, use that book for additional practice. I would also consider the OG Verbal and OG Quant, as those collections provide additional problem practice. This might seem excessive, but it will help your performance.