Ian,
On the bottle of Aeroshell sport plus 4 there are, as you said, two dates.
One is the born-on date and the other is the expiration date. They are two years apart.
If you read further down, it states a retest date of four years from the born-on date.
So what are they really saying? If it expires, like they say, two years from the date of MFG, then why list a retest date of four years from the born-on date.
Seems like the oil should be good for awhile after the expiration date. This is only my opinion, with no facts to back it up. It just makes sense to me.
There has been much discussion of this topic on another forum.
Rich