Adding sale 1 to the range.

https://backpack.tf/item/4621072860

Sale 1) Sold for 21 Keys

https://backpack.tf/profiles/76561198401924250#!/compare/1526688000/1527120000

Sale 2) Sold for a Death at Dusk Stormin' Norman (30 Keys)

https://backpack.tf/profiles/76561198159587792#!/compare/1527033600/1527120000

Can't actually confirm this sale. Ignoring.

Sale 3) Sold for a Spec KS Aussie Knife (~17 Keys) + 6 Keys

https://backpack.tf/profiles/76561198159587792#!/compare/1527897600/1528070400

17 + 6 = 23 Keys

Sale 4) Bulk sale

https://backpack.tf/profiles/76561198254620348#!/compare/1529539200/1529625600

Sale 5) Sold + ~1.5 Keys of Items for a SBTWC Nanobalaclava (40.5 Keys)

https://backpack.tf/profiles/76561198255903931#!/compare/1529539200/1529625600

https://backpack.tf/profiles/76561198369075257#!/compare/1529539200/1529625600

High outlier.

Sale 6) ?

https://backpack.tf/profiles/76561198369075257#!/compare/1530403200/1530576000

Sale 7) Bulk sale

https://backpack.tf/profiles/76561198255903931#!/compare/1530835200/1530921600

Sale 8) Sold for $40 when Keys were ~$1.96 each

https://marketplace.tf/items/15143;5;u702;w4;pk81;kt-1

40 / 1.96 = 20.4, which rounds to 20 Keys

Low outlier.

https://imgur.com/a/X3AJ7RL - Buyer at 20 Keys

https://backpack.tf/u/76561198002757046