Proof:

http://www.tf2outpost.com/trade/15294325 - Sold, probably for more than 12 because a 12 keys offer was hidden by owner and the one who bought it offered 14 to: http://www.tf2outpost.com/trade/14905594

http://www.tf2outpost.com/trade/15282671 - Sold Grenade with Airborne (~0.9), Soldiers (~0.33) and Dominations (1.5 - 2) for 16, since parts alone cost ~4 keys the grenade sold for more than 12

http://www.tf2outpost.com/trade/14973136 - Sold Grenade with Gib (~0.33), Uber Kills (~0.1) and Engineers (~0.15) for 14 keys, since parts are LESS than a key this sale is even above 13, it sold to: http://www.tf2outpost.com/backpack/36144

http://www.tf2outpost.com/trade/15222440 - Sold for 13

http://www.tf2outpost.com/trade/15289127 - Sold for 13 in less than a day

http://www.tf2outpost.com/trade/15309674 - Sold for 13 in 7 hours

http://www.tf2outpost.com/trade/15321218 - Sold for 13 in less than an hour (showed by trade.tf)

http://www.tf2outpost.com/trade/15282671 - Sold for 14 in less than 20 hours

http://www.tf2outpost.com/trade/15265617 - Sold for 14 without a bump

I usually don't use parts attached but the ones I used were easy to see as above 12 and above 13

Not MANY solds but keep in mind over half are in sets/parts

Since 12 is still possible I leave it in range but 13 is also possible

Extra Proof:

http://tf2tp.com/trade.php?trade=9860428 - Sold for 13

http://www.tf2outpost.com/trade/15304792 - Sold for 13 in less than a day

There are also some solds at 13 through backpack.tf, I won't show pictures so you can just ignore it but it's there in trade.tf