This is true, but while OEMs quote flywheel figures people will strive to "guess" what theirs is compared to the OEM figure. This is why DynoDynamics seem to always give you figures quoted at the fly - and more savvy members request at the wheel.
I didnt have mine dyno'd before I started fitting mods so we had no way of knowing what it was compared to stock. Mark had a stock car in which dyno'd at 275@hubs (293 with drop-in filters, exhuast and UpRev), mine dyno'd at 303 with exhaust and intakes, it gained a further 5HP with UpRev (quite a bit more low down grunt though). So make of all that what you will