After a search spanning several years I finally got the last Prisoner Promo from Cornerstone that I needed The b Promo 512 Prefix.

So I now have all 6

• Promo a grey-blue back 512/512 prefix
  
• Promo a grey-blue back 520/520 prefix
  
• Promo a Blue back 520/512 prefix
  
• Promo b 520/520 prefix
  
• Promo b 512/512 prefix
  
• Promo IT-8
  

This is all in accordance with the PCE, except that it says that the promo a blue back has a just a 512 prefix while NSU agrees with me that it is a 512/520.
Anyhow, The reason for this post is that NSU also lists a Promo a glossy.

Is this another promo, a 7th or is it an error?