If there were promo copies then the song received airplay, and likely was tracked on some chart other than the Hot 100. The problem we have today is that most artist pages primarily use Billboard. This particular song was before R&R.
Gonna make me work for this, huh?
LED ZEPPELIN IV was released in mid-November of 1971. It debuted at #36 on Billboard's LP chart the week of November 27.
The first single from the album was "Black Dog", which debuted at #67 the week of December 25. The follow-up was "Rock and Roll".
Billboard did not have an airplay chart at that time. I just looked.
But none of that matters, because---
A) We weren't talking about airplay charts, we were discussing the Hot 100 and the Beatles holding the top five positions with singles, not LP cuts (I parenthetically gave "Stairway to Heaven" as the example of how a hugely popular LP cut doesn't make the Hot 100 because that was a singles chart).
B) The first time Atlantic pressed "Stairway to Heaven" in the United States as a promo-only 45---was 1976. And the story behind that:
By '76, "Stairway" had become a hot item in most Top 40 stations' Gold libraries. The original copies of LED ZEPPELIN IV were five years old and had seen better days. Atlantic was getting a large number of requests from Top 40 stations to re-service the album. The promo copies were gone, and they would have had to take them from stock---and the album was still selling well. So Atlantic had a limited run of 45s made--and labelled them "Atlantic Promotional EP"---with "Stairway" on both sides.
View credits, reviews, tracks and shop for the 1976 Vinyl release of "Stairway To Heaven" on Discogs.
www.discogs.com
It was library service, not an official single release, and so, "Stairway to Heaven" was not considered a single in the US, but an album cut, and as such, did not chart on its own in the US until Billboard's downloads chart---in 2007.