tiny tiny error, but a potential biggee

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Found HPD 2473931, a $5 note with face position number 48.  Logically, the back position number should be 11.  Instead, I found a 1 with a blob of blue ink to the left of it.  No big deal, right?  The blob is where the first 1 should be.  However, the blob is too small to cover up the entire digit.  The first 1 is definitely missing.  I wonder if this means the plate is broken?  A search of notes with the HPD prefix might provide more clues as to what is going on here.

Years of searching through tens of thousands of notes have not yielded anything like this until now.  My scans below are not great, and if there's interest in this topic, I will attempt a re-scan.

{http://img69.imageshack.us/img69/1808/hpd2473931.jpg:http://img69.imageshack.us/img69/1808/hpd2473931.th.jpg}

{http://img38.imageshack.us/img38/3310/hpd2473931c.jpg:http://img38.imageshack.us/img38/3310/hpd2473931c.th.jpg}

From what I can see on the scan it does look like the number "1" did not print
Guess I will have to keep my eyes open

I checked a bunch of my HPD notes (mainly starting in the 7xxxxx range) and they have plate 15 marked clearly, so you might have something there........only a certain range/series

... perhaps this is something similar to the 'missing circle' variety, attributable to a plate anomoly rather than an error