If a sonogram due date matches lmp due date, does that mean ovulation was right on time of regular cycle, and not earlier?

Depends: If at least two sonograms were done from 6-9 weeks that correlate, i would say your dates are +/- 1 day and you could pinpoint ovulation with that accuracy. If you only had one sonogram in that range it would maybe be +/- 3days. Other factors are the interpretation by the OB person. Did the sono agree exactly or within some "tolerance" range. Comments above are for "right on" dating.