try at least 4, and to be clear I am not talking about how the 4 mount holes are configured with regard to each other, but how each set (usualy the rear) is spaced with regard to other important points on the rifle. and i'll elaborate on what i mean below.
I spent most of the past two years working the gun counter at a sporting goods store with a policy of "Buy the rifle, scope, or mounts with us and we'll mount everything and boresight it for free, or $15 if you bring in all outside parts".
I can't count the number of savage made centerfire rifles, mostly long action stevens 200s, i've (re)scoped or simply installed mounts on (Leupold, and Redfield branded weaver types being our most common brands). on about 1in5 of them the "Savage" marked bases flat out would not fit without interfering with the operation of the rifle. Most common issue was that the rear base would either stick out over the back of the receiver ring blocking bolt manipulation, or when turned the other way would hold the ring at a slight angle and a scope wouldn't sit flat in the ring.
about a year and a half ago our Dept manager received notice passed down from Leupold that effectively said "Try the "savage" bases first, if that don't work sometimes the "A-Bolt" mounts will work. If neither works out. You're on your own".
specific case, we had a guy come in at 8am one morning who wanted as many long action Stevens rifles as he could get in "any caliber they make 'em except 7mm Mag", but if and
only if we could mount and boresight a scope on every one of them, and have him out the door before noon when he had to leave to prep things for a Youth hunt. we had 10 rifles that met his caliber needs, 4 of them wouldn't take the same mounts as the other 6.
to be absolutely clear that's ten rifles with supposedly identical receivers (5 270s and 5 30-06s) with 4 of them needing a different base set from the others (the A-Bolt base worked).
strangely through all this I know that the spacing of the holes in relation to each other hasn't changed, since a one-piece base would fit +95% of the time as long as we pulled the right one for the action length (barring the flat Vs round top issue) we only had one incident where a 1-piece Leupold base wouldn't fit, and I feel that that one was an out of spec base. The middle hole in the base was out of line with the receiver hole enough that you could see it wasn't lined up, much less try and start the screw
