It is typical to consider a relay with a different of any 4 people a different relay.
Likewise, if you keep the same 4 people and they run a slower time than their best, but still top 10, you wouldn't put that time onto the list.
As an example:
So if relay "A" in 2012 consists of tommy, timmy, tony, and toby and runs 42.2 in the 4x100, getting 4th all time, you would put them into that spot (4th) on the all-time list.
Two weeks later, still in 2012 season, relay "B" runs with Tommy, Timmy, Tony, and Jack (so 3 of 4 legs the same) and runs 42.1 for the new 4th all time. You would then put them onto the list, bumping relay A down a slot, even though 3 of 4 people are the same
2 weeks later, still in 2012 season, Tommy, Timmy, Tony, and Toby run again (relay A) and run 42.4, which is 6th all time on your list. You would not put them onto your list, because this relay has a faster time already on the list. It is not traditional to make an all-time list with the same person (or exactly same 4 person relay) on there multiple times.
Now go forward a year to 2013 season. Tommy, Timmy, Tony, and Jack (2012's "B" relay) now run 42.4, which again would be 6th all time. You would not put them onto the list, because the previous year these exact same 4 athletes ran faster for 4th all time.
Make sense?