Including 39 per Polar's advice.

https://backpack.tf/item/1069339841

Sale 1) Sold for $66 when Keys were ~$1.82 each

https://marketplace.tf/items/tf2/339;5;u36

https://marketplace.tf/items/tf2/5021;6

https://imgur.com/a/iQQopHj - Capped by the Buyout of 33 Keys

Sale 2) Quicksold for 21 Keys + 15 Refined?

https://backpack.tf/profiles/76561198122096342#!/compare/1562630400/1562716800

Low outlier if so, quicksell either way.

Sale 3) Probably sold for 35 Keys

https://backpack.tf/profiles/76561198847672167#!/compare/1564099200/1564617600

https://backpack.tf/profiles/76561198101590387#!/compare/1564704000/1564790400

Sale 4) Sold for a Spec KS Aussie Rocket (~34 Keys)

https://backpack.tf/profiles/76561198101590387#!/compare/1564876800/1564963200

https://backpack.tf/profiles/76561198043992035#!/compare/1564876800/1564963200

https://backpack.tf/item/1461870727

Sale 5) Sold for $69.99 when Keys were ~$1.82 each

https://marketplace.tf/items/tf2/339;5;u36

https://marketplace.tf/items/tf2/5021;6

https://imgur.com/a/Wdcd7rf - Capped by the Buyout of 35 Keys

Sale 6) ?

https://backpack.tf/profiles/76561198402650545#!/compare/1561420800/1561852800

Sale 7) Sold for 36 Keys

https://backpack.tf/profiles/76561198112281935#!/compare/1565136000/1565222400

https://backpack.tf/item/2880490653

Sale 8) Sold for an Orbiting Fire Le Party Phantom (33 Keys)

https://backpack.tf/profiles/76561198280357510#!/compare/1558915200/1559088000

The Phantom was freshly in-date at the time of the sale.

Sale 9) ?

https://backpack.tf/profiles/76561198205939253#!/compare/1560729600/1560816000

https://backpack.tf/profiles/76561198051356793#!/compare/1558828800/1560816000

https://backpack.tf/item/1122480017 - Duped

Sale 10) ?

https://backpack.tf/profiles/76561198080179568#!/compare/1560643200/1560729600

https://backpack.tf/profiles/76561198299425567#!/compare/1560729600/1560816000

https://backpack.tf/item/1362154144 - Duped

Sale 11) ?

https://backpack.tf/profiles/76561198021272428#!/compare/1558742400/1558828800

https://backpack.tf/profiles/76561198132827798#!/compare/1558828800/1559606400

https://backpack.tf/item/1173557655 - Duped

Sale 12) ?

https://backpack.tf/profiles/76561198171490163#!/compare/1559260800/1560124800

https://backpack.tf/profiles/76561198134512931#!/compare/1559433600/1559520000

Sale 13) Quicksold for 30 Keys + 17 Refined

https://backpack.tf/profiles/76561198134512931#!/compare/1559520000/1559606400

https://backpack.tf/profiles/76561198219263116#!/compare/1559347200/1559606400

Sale 14) Sold for 34 Keys

https://backpack.tf/profiles/76561198219263116#!/compare/1560297600/1560384000

Sale 15) ?

https://backpack.tf/profiles/76561198117971944#!/compare/1560297600/1560384000

Sale 16) Sold for 31 Keys

https://backpack.tf/profiles/76561198337734785#!/compare/1560384000/1560470400

https://backpack.tf/profiles/76561198080714795#!/compare/1560384000/1560470400

Low outlier.

Sale 17) Sold for 19 Keys + Spec KS Aussie Minigun (~18 Keys)

https://backpack.tf/profiles/76561198080714795#!/compare/1560470400/1560556800

https://backpack.tf/profiles/76561198320030042#!/compare/1560470400/1560556800

19 + 18 = 37 Keys

Sale 18) Sold for a Purple Energy Buckaroos Hat (27 Keys) + 3 Keys

https://backpack.tf/profiles/76561198320030042#!/compare/1560470400/1560556800

Low outlier.

Sale 19) Sold for a Green Energy Copper's Hard Top + 15 Keys

https://backpack.tf/profiles/76561198267189538#!/compare/1560470400/1560556800

https://imgur.com/a/0GdRrkJ - Capped by the Buyout of 34 Keys

Sale 20) Sold for 35 Keys

https://backpack.tf/profiles/76561198080714795#!/compare/1560556800/1560643200

https://backpack.tf/profiles/76561198007206529#!/compare/1560556800/1560643200

https://backpack.tf/item/497891141

Sale 21) ?

https://backpack.tf/profiles/76561198337734785#!/compare/1559347200/1559433600

https://backpack.tf/profiles/76561198030091664#!/compare/1559347200/1559433600

Sale 22) ?

https://backpack.tf/profiles/76561198030091664#!/compare/1559347200/1559433600

https://backpack.tf/profiles/76561198190124379#!/compare/1559347200/1559433600

Sale 23) Sold for 33 Keys

https://backpack.tf/profiles/76561198148836514#!/compare/1562198400/1562284800

Sale 24) Sold for 35 Keys

https://backpack.tf/profiles/76561198354979270#!/compare/1562544000/1562630400

Sale 25) ?

https://backpack.tf/profiles/76561198258042183#!/compare/1564704000/1564963200

https://backpack.tf/profiles/76561198068732040#!/compare/1564876800/1564963200

Sale 26) Sold for 35 Keys

https://backpack.tf/profiles/76561198068732040#!/compare/1565136000/1565222400

https://marketplace.tf/items/tf2/339;5;u36 - Sold for $63.99 when Keys were ~$1.84 each, $50 (low), and $69.99 when Keys were ~$1.81 each

https://marketplace.tf/items/tf2/5021;6

63.99 / 1.84 = 34.77, which rounds to 35 Keys

69.99 / 1.81 = 38.67, which rounds to 39 Keys

Duped sales are basically the same as Clean, so they're included.