By my counting then, the 20th (which would be the 2nd 10th) would fall on the last day of a visible waning crescent.
Wouldn't the "earlier tenth" (20th) look like the moon on the above charts on Dec. 13 or 14th? The Noumenia seems to have started when the "first sliver" of the new moon was visible.
That's what I determined (approximately the geometry of my current profile picture).
Kalosyni I believe the picture you shared is a waning crescent just a few days away from a new moon, which should occur on the first and last days of the month (assuming it began on a new moon and is 30 days long).