Here is additional proof from the last suggestion that ends in this range

https://marketplace.tf/items/tf2/30404;5;u60

At the time this suggestion was created, there were (indate) marketplace.tf sales at:

$19.44 / $1.69 = 11.50 keys

$15.2 / $1.69 = 8.99 keys

$19.44 / $1.69 = 11.50 keys

$19.44 / $1.77 = 10.98 keys

$24 / $1.90 = 12.63 keys

$23.66 / $1.96 = 12.07 keys

$23.99 / $1.99 = 12.06 keys

$30 / $2.00 = 15.00 keys

$23.83 / $2.00 = 11.91 keys

Non-marketplace.tf sales:

https://backpack.tf/profiles/76561198311498888#!/compare/1591488000/1591574400

https://backpack.tf/profiles/76561198972294135#!/compare/1591488000/1591574400

https://stntrading.eu/item/tf2/Unusual+Dead+Presidents+Aviator+Assassin

10 keys match, was probably 10 keys 48 ref

Your purchase at 11 keys

https://backpack.tf/profiles/76561198278170243#!/compare/1591401600/1591488000

https://backpack.tf/profiles/76561198241082598#!/compare/1591574400/1591660800

https://backpack.tf/profiles/76561198132155559#!/compare/1591574400/1591660800

Bulk for GE Toe (supports large drop)

https://backpack.tf/profiles/76561198132155559#!/compare/1591660800/1591920000

Bulk for CH Bonk (supports large drop)

https://backpack.tf/profiles/76561198340434037#!/compare/1592006400/1592092800

Bulk QS

That gives sales at:

9

11 (x2)

12 (x5)

13 (x2)

15

https://imgur.com/a/MLKU1b8 - 2 sellers at 11 right now.

Safe to call 9 low and 15 high here