Well, Deep Cert has spoken and found us lacking

Actually, plate 12 is really hard to plate. I have never heard of anyone who was actually really good at plating material from it.
Anyway, Deep Cert says this is position 21R12.
Deep Cert:
"The posted stamp is actually 21R12, which also has that blur off the left plume. Problem is Neinken did not show it on his mat. Here's my copy of 21R12 for comparison."

Deep Cert:
"61R12 has a very large guide dot inside ornament R, as shown in Neinken. Attached is a scan of orn R from a copy of 60R12. Neinken shows similar dots on eight other positions from Plate 12. Plate 11 also has some of these."

"Also note the weak right plume on 21R12 as shown in Neinken. The posted stamp has this feature covered with cancel, unfortunately."
And I'm going to post this quote, also from Deep Cert, to illustrate some of the complexities with plate 12. I think its revealing:
"I hate plate 12. My collection of them fits on one album page, mostly centerlines. I have scans of close to 100 plate 12 stamps I can't plate. "