Samantha Carter explains in the pilot that because of the expansion of the universe, stars are moving away from each other and a correction needs to be made to the dialing protocol to account for this. She further states that dialing for nearby gates (such as Abydos, and later we learn also Heliopolis) is unaffected since stars further away are receding from earth more rapidly than nearby stars. However, isn't the expansion of the universe observed between galaxies clusters and not between individual stars within a galaxy? The stars of the milky way are not receding from each other, they are all at a (roughly) fixed position relative to each other as they orbit the supermassive blackhole at the center of our galaxy. So why would any correction need to be made for dialing between gates in the milky way?
(And further, the expansion of the universe is an effect seen at even larger distances than galactic clusters, so one wouldn't think this effect impacts dialing within the local group; therefore, not meaningful even for dialing to Pegasus. Though, of course, galaxies in the local group are moving relative to each other... a fact we will be painfully aware of in 2.5 billion years when the Adromeda and Milky Way galaxies collide.)
Edited to Add: Certainly stars in the galaxy are moving relative to each other, and this might well account for some of the addresses not working. However, Carter and Daniel Jackson explicitly state that it is the expanding universe causing the dialing to be off, which is why they can (relatively) easily correct for it:
Carter: According to the expanding universe model, all bodies in the universe are constantly moving apart.
Jackson: But why does it still work between Abydos and Earth?
Carter: Abydos is probably the closest planet in the network to Earth. I mean, the closer they are, the less the difference in the relative position due to expansion. The further away, the greater the difference.
If the adjustment had to do with intragalactic stellar movement, then closeness to Earth would not be as relevant. (Though, of course, the closer to Earth the less likely some other massive body has passed into the path between Earth and the other planet which might make it less likely that an adjustment is needed in dialing).
Also, I discount things like the motion of the planet around it's star since this would have impacted dialing Abydos and Heliopolis as much as anywhere else over thousands of years (presuming they orbit their stars at speeds at least comparable to that of earth, which seems reasonable given that their environmental conditions are very similar to earth).