Partial answer only, to help others give a better answer.
One question that is raised here is whether teens give accurate answers in surveys. One possible measure of inaccuracy is "test/retest" inconsistency. That is, if you ask the same person the same question again, do you get the same answer?
Test–Retest Reliability of Self-Reported Sexual Behavior, Sexual Orientation, and Psychosexual Milestones Among Gay, Lesbian, and Bisexual Youths Eric W. Schrimshaw, Margaret Rosario, Heino F. L. Meyer-Bahlburg and Alice A. Scharf-Matlick, ARCHIVES OF SEXUAL BEHAVIOR, Volume 35, Number 2, 220-229, 2006. DOI: 10.1007/s10508-005-9006-2
They asked 64 youths (aged 14-21) recruited from GLB-focussed organisations about their sexual identity twice, two weeks apart, and compared the answers.
They found sexual identity had Cohen's Kappa value of 0.89, which is a strong indication that they got very similar results - but not identical ones.