I'm going on what I've been told by a Mastergunsmith I know who builds well over 100 Savage rifles a year.
According to him, you used to have to true the bolt face on the old Savage rifles, since the Accustock and since Savage has re tooled, the bolt faces are so true that the very few times he has found one that is not true, he just throws it away and puts another one on.
So there is now a difference. I don't know if Savage makes the bolt head or not, I can't believe they wouldn't, but I do trust the word of the smith.
The tollerances on all parts of the action are now much better, far less metal needs to be removed from the face of the action to true it, same goes for the bolt lugs. Savage has made a pretty big improvement. Replacing almost all their CNC machines and now tracking exactly how many pieces have been cut with each cutter, so a new cutter can be installed has made a big difference in the precision in which their rifles are made. My hat is off to Savage for making these kinds of changes. That's why they are on top and will stay that way.

This is not to say that there may not be some variation in bolt head thickness. This depends on when the rifle and bolt head were made. One should expect to have to change the headspace a little anytime a bolt head is replaced. There are just too many variables that will require the H.S. to be corrected.
John K