Plate Number Reissue?

I recently got this block. Why is it a reissue block?

I'm sure Scott has much more to say, but SG identifies five versions:

9 Dec 02 - wmk double-lined USPS in sheet, in pale ultramarine, ultramarine and blue. P12.
11 Jan 11 - wmk single-lined USPS in sheet, in ultramarine, pale ultramarine and deep blue. P12.
Sept 14 - wmk single-lined USPS in sheet, pale ultra,arine. P10.
19 Oct 16 - no wmk. Pale ultramarine or ultramarine. P10.
2 May 17 - no wmk. Ultramarine, grey-blue or violet-blue. P11.

Geoff

My Scott Specialized Catalog explains it like this:

Cool. I see that in my scotts now also. I was looking for something in my Durland but did not see it.
Thanks

Ray.... if you have the 2012 Durland, it's on page # A19... also on page # A17 in the 2008 issue...