The Special Printing was just that, with printing plates carefully cleaned, the printing done with care. The engraved lines show very distinctly. At the left and right sides, there are short horizontal lines that should be very, very separate and clear. The vertical shading lines below the ribbon are similarly distinct. Compare with the first 2 examples here (other scans are mostly slightly lower quality):
http://www.usphila.com/us/stamp/pri...t-172-page-1A further test is that nearly all Special Printings were cut apart from the sheets with scissors.
The engraving details in yours are either somewhat muddy or worn, therefore unfortunately not a #172. Continental had a thick paper; maybe that's what you have.
Fakes probably exist but many more have been just misidentified more than anything else.