On the CommonApp and JHU’s website, it says that JHU requires 2 letters of recommendation from two teachers. But I saw on some other forums that you are allowed to submit additional letters from mentors, coaches, etc. Is this true?
If the university and their website say 2, I would follow that and not what someone else says. If an AO is reviewing 50 applications per day (and some do more), they don’t have the time to go through extraneous material.
You’re sometimes “allowed” to by some schools, but they generally need to be something that provides a unique story not told elsewhere, or something else extraordinary. AO’s aren’t big fans of increased workload just to hear the same story again.
If a school doesn’t state that it will accept optional letters and specifically says to send two, then only send two.
General advice for the future - believe what it on a school’s admissions office website over “I saw on some other forums”.