Marvel did not publish sales figures for the title for a very long time, but by the time it did, Iron Man was a mid-range seller along with the other Avengers titles. The series peaked above 200,000 copies in the mid-1980s during David Michelinie and Bob Layton's first run on the title; it approached that level again several times before collapsing during the market recession of the mid-1990s.
Marvel addressed the decline then — and several more times — with the same strategy: restarting the series from a new #1. The "Heroes Reborn" volume 2 and the "Heroes Return" volume 3 resuscitated sales (this run included John's year on the title), as did the Warren Ellis Volume 4 in 2004. But unlike with Amazing Spider-Man and Fantastic Four, Marvel has yet to permanently reunify the series into a single numbering. The current flagship Iron Man title, Invincible Iron Man, shipped its 25th issue in April.
It's apparent that the same postal permit was used for the series during its first three volumes; subscribers for the previous series were simply rolled into the next one. However, we don't know if Statements of Ownerships have appeared in the post-2004 versions, so we're reluctant to call the file on the original title closed. If you've spotted Statements in the later runs, please let us know.