The atlas holds two entries for the word apostle, and the reason is a genuine disagreement rather than a filing decision. The Latter-day Saint claim is that this is the New Testament apostleship restored, conferred on Joseph Smith and Oliver Cowdery by Peter, James and John as resurrected beings, and continued by unbroken ordination since. On that account there is one office and it went out of use for seventeen centuries.
Other Christian bodies reject the claim by two different routes. Most Protestant traditions hold that the apostleship was unrepeatable, tied to men who had seen the risen Christ, and that it ended with them. Catholic and Orthodox teaching holds that it continues, but in the episcopate, through a succession that never lapsed, so the Latter-day Saint claim fails at its first premise rather than at its last. Both positions make the modern Latter-day Saint apostleship a new office bearing an old name.
The atlas records the claim as a claim and keeps a separate entry, because the two offices as they are actually lived have very little in common. A first century apostle was an itinerant witness with no institution behind him. A modern Latter-day Saint apostle is a lifetime officer of a corporation, ordained in a settled sequence, with an administrative portfolio and a place in a fixed order of succession. Describing them in one entry would serve a reader badly whichever theology they hold, and would quietly make the atlas take a side.