Credits to Metal Core for the first sales and King for finding the others.

Metal Core:

Smoking Das Gutenkutteharen

Item 1:

History:https://backpack.tf/item/3404047451

Sale 1: 21 Keys 25 Ref

Buyer: https://backpack.tf/profiles/76561198110013221#!/compare/1683244800/1683676800

Seller:https://backpack.tf/profiles/76561199189722140#!/compare/1683590400/1683676800

Sale 2: Untrace

Buyer: https://backpack.tf/profiles/76561198057412106#!/compare/1686096000/1686182400

Seller:https://backpack.tf/profiles/76561198110013221#!/compare/1685318400/1687392000

Sale 3: Bulk for Steaming Mining Light

Buyer: https://backpack.tf/profiles/76561199133022139#!/compare/1686182400/1686355200

Seller:https://backpack.tf/profiles/76561198057412106#!/compare/1686268800/1686355200

Round to 21 Keys

21 Keys

King:

19 keys

https://backpack.tf/profiles/76561199133022139#!/compare/1688169600/1688860800

https://backpack.tf/profiles/76561198120332855#!/compare/1688169600/1688256000

Then dumped to bot for ~18 it seems

https://backpack.tf/profiles/76561199388511269#!/compare/1688515200/1688601600

https://backpack.tf/profiles/76561198120332855#!/compare/1688601600/1688774400

https://next.backpack.tf/classifieds/snapshots/Smoking%20Das%20Gutenkutteharen/64a6c3170e5c23dbfc035163

18 is untraceable, so I would at least include 19 in range.

Taking 19-21