I don't know I have seen 2 Hifonics 1500's metered and both their output was significantly different maybe 150 watts. Just what we noticed, could be nothing or everthing.
On this amp and many more a 2 volt drop can make a big difference. Most cars run somewhere in the middle @13.8 and that is why the 14.4 is misleading, always take a good 10% off or so on the RMS when they rate the amp at 14.4.