I added one assumed contour for Devils Thumb but no more, because a single 60m gets you back to the saddle (60/2*3.28=98.4'; that's also at an angle, not vertical, so make it 80'). It's actually debatable whether there is a missing contour or not, because a single closed contour essentially already covers the optimistic end of the spectrum (12040 low to 12120 high = 80')
When we climbed it, we did it in two raps because the 60m didn't quite reach. Maybe we took a different line down though and as you said, it's at an angle.
Ormes list Devils Thumb as 12,150 feet, which would if accurate, would be 90' (which is not far from 80), but I don't know where Ormes got the altitude.
It seems that Ancient Art is a formation with multiple summits, though, and it appears that the corkscrew isn't the highest (Desert Rock probably clarifies this, but I don't have it in front of me).
The highest summit of Ancient Art is the northern middle summit; the one with the sand pipe sticking up as can be seen in the link:
https://books.google.com/books?id=YJuqs ... II&f=falseDesert Rock III:
https://books.google.com/books?id=YJuqs ... mb&f=falseI guess either way it would be unranked, but I assume it would have over 80' prominence.
Some rock towers may be ranked though that are missing on the list. Standing Rock, in Monument Basin, for example, is said to be "almost" 350' high.
http://www.summitpost.org/standing-rock/716910There are actually many free standing towers in the basin that
may have 300' prominence, but it's not something that can be determined by looking at the topo maps.
Towers such as the Pixie Stick wouldn't make the 300' prominence criteria, but they do demonstrate why a topo map is useless in trying to determine the prominence!
LOJ (understandably!) list only two summits in Monument Basin that have over 300' prominence, but I'm guessing that there are actually more that would qualify. Other than with a survey, laser, shadow measurement with a trigonometric calculation, or a climber using a GPS, it would be hard to determine the prominence.