The 2012 Topps Red Border parallel are Target exclusive, as you probably know.
Blue border Walmart exclusive, purple border Toys R Us Exclusive.
Gold sparkle parallel came in hobby shop packs.
Gold bodrder serial # /2012 for the flagship set and also the update set, were "forgotten about [?,] and then inserted into all formats of Update.
Generally speaking the various parallels came out at a rate of 1 card per 3 packs for a 10 card pack, or 1 per pack for larger format packs.
I think most people in the hobby consider the lowest production / rarest parallel to be Toys R Us, and then the Target. Hobby shop and Walmart have the highest production runs. My personal guess is that the Target red border parallel production run was something in the neighborhood of 5,000 +/-, but don't ask me how I got that number, just pulled it out of thin air.
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