Item 1

https://backpack.tf/item/7956997157

Sale #1

Sold for 15 keys (ID "13088355727" of the unusual match)-

Seller: https://backpack.tf/profiles/76561198252071476#!/compare/1684108800/1685404800

Buyer: https://backpack.tf/profiles/76561198810676594#!/compare/1685318400/1685491200

Sale #2

Bulk sale-

Seller: https://backpack.tf/profiles/76561198810676594#!/compare/1685491200/1685577600

Buyer: https://backpack.tf/profiles/76561198850121720#!/compare/1685404800/1685491200

Sale #3

Untraceable-

Seller: https://backpack.tf/profiles/76561198850121720#!/compare/1685923200/1686009600

Buyer: https://backpack.tf/profiles/76561198106288924#!/compare/1671580800/1691020800

Sale #4

Untraceable-

Seller: https://backpack.tf/profiles/76561198106288924#!/compare/1691020800/1691539200

Buyer: https://backpack.tf/profiles/76561199026390261#!/compare/1691193600/1691452800

Marketplace.tf Sales

https://marketplace.tf/items/tf2/30045;5;u58

MP.TF Sale #1

Sold for $39.99 on June 8, 2023

Keys @ $1.99

39.99/1.99 = 20.10ish keys

MP.TF Sale #2

Sold for $39.99 on July 24, 2023

Keys @ $1.95

39.99/1.95 = 20.51ish keys

[b]Sales @ 15. 20, 21

Don't see any reason to not include 15 here

Taking 15-21[b/b]