A larger scan would help but I think your assessment is correct. I think I can see the plating marks in the top left ornament and the "G" in postage which are also shown in the Ashbrook & Neinken plating diagrams.
I've only made a few attempts to plate so far. I'm trying. The Stamp Smarter database was great for this. txstamp narrowed it down to one plate, ten stamps to check. With the multiple scans for each position, interestingly I found the Neiken images the easiest to use. Anyway, thanks all.