I have no idea, just that mine has always been +42 no matter what firmware it used, I checked again just after I posted to see if the firmware had ever made any difference to see if that could be the reason ...but not... this is the hardware we are talking about after all.
The only other thing I could think of is if it was some sort of re badge job ? I also have the 7170a (same drive just with DVD-RAM) and I am sure that was the same, its not in a working box ATM so I cant test it.
..or that the other poster had the profile of another drive loaded at the time they checked, but I have just put your title into google and found some logs posted by someone saying his is 66 but then his drive does not report the same as mine (no C2 and no cache ...it has both) and also the http://www.accuraterip.com/driveoffsets.htm database says +48. Wonder if firmware could really do something, I have only had 3 changes and I have stuck with Liggy's 1.12 bitsetting.
My drive[s] was one of the first, so could they have changed something, when the jobs finish running on the box with the 5170 I will make up another disk and re-check it. But I have a 6+ hour run time ATM.