Sale 1:

https://backpack.tf/profiles/76561198045883624#!/compare/1588291200/1588377600 - Sold for Blizzardy Storm One-Man Army (11.5, rounding to 12)

https://backpack.tf/profiles/76561198109611180#!/compare/1587686400/1588377600

Blizzardy Storm One-Man Army: https://backpack.tf/suggestion/5f085b0ba36328313009c561

Sale 2:

https://backpack.tf/profiles/76561198109611180#!/compare/1588896000/1589068800 - Bulk.

https://backpack.tf/profiles/76561198151835897#!/compare/1588982400/1589068800

Sale 3:

https://backpack.tf/profiles/76561198348707897#!/compare/1583971200/1591747200

https://backpack.tf/profiles/76561198452038526#!/compare/1589068800/1594080000 - Bulk?

Sale 4:

https://backpack.tf/profiles/76561198095022965#!/compare/1588204800/1588377600 - Bubbling Brass Bucket (11) + 3 keys = 14 keys

https://backpack.tf/profiles/76561198102133055#!/compare/1586304000/1588636800

Bubbling Brass Bucket: https://backpack.tf/suggestion/5f085cd39f8baf403b7ac350

Sale 5:

https://backpack.tf/profiles/76561198102133055#!/compare/1591228800/1593820800 - Sold with 1 key for Kill-a-Watt Front Runner (Use there)

https://backpack.tf/profiles/76561198231709968#!/compare/1591142400/1591228800

Sale 6:

https://backpack.tf/profiles/76561198231709968#!/compare/1591228800/1591315200 - ?

https://backpack.tf/profiles/76561198799211837#!/compare/1591401600/1591488000 - ?

Sale 7:

https://marketplace.tf/items/tf2/31074;5;u58

May 1 - $18 / $1.85 = 9.73 keys = 10 keys, couldn't find b/o

Jun 6 - $21.99 / $1.99 = 11.05 keys = 11 keys, couldn't find b/o

Sales:

10

11

12

14

~10-14