Yes, the official app is the official guide in electronic format.
So the questions in OG 12
and the app overlap 100%. They have not released the OG 13
in electronic format for some reason.
If I can do shameless plug, would recommend the GMAT Toolkit app
by Walker - it comes with 990 questions and allows you to download additional questions for free for up to 3,000 questions.
So they contain the same questions, except for 7 that are missing from the official app? Because the app only has 223 problem solving questions whereas the OG has 230 of them.