That is entirely possible. I can surmise that manufacturers implement different circuit designs in the pre/pro stage so that even the volume pot can behave differently and the preamp output stage can likewise have varyng signal levels fed to the amplifier section, even if they have the same volume position.
Those volume calibration sometimes mean little. The zero db setting should roughly correspond to a signal level at the preamp stage that can drive the power amp to full power as rated. However, some manufacturers can deliver a preamp signal level much higher than in other brands so that their receivers can sound louder for the same volume setting. ("hey, if it can sound that loud at that level, wow, imagine how loud it can get at full!!!) Remember, too, that no salesman will allow their wares to be driven at full volume in any mall showroom. This is actually one of my complaints about receivers. As a consumer, you really have no idea if the amp section is getting overdriven by an overly jealous preamp output within that receiver. You really wouldn't know if the preamp has unity gain or has some gain values that can give the impression the receiver has more loudness than another brand of the same power in the same volume setting.
But given the same power rating at the same measurement condition, (i.e, full bandwidth, all chanels driven, at the same THD/IM level, etc.) and assuming the volume settings on the pre/pro stage are the same, the preamp output signal level the same, there shouldn't be any difference.
