6 sales

1) 20 keys

https://backpack.tf/profiles/76561198302774496#!/compare/1551657600/1551744000

https://backpack.tf/profiles/76561198339381843#!/compare/1551744000/1551830400

20

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2) Disco Beat Down Brass Bucket (22)

https://backpack.tf/profiles/76561198176500230#!/compare/1550620800/1550793600

Bucket sold for $38.65 on March 1st, keys were $1.78

https://marketplace.tf/items/30969;5;u62

38.65/1.78 ≈ 22 keys

22

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3) 20 keys

https://backpack.tf/profiles/76561198074424269#!/compare/1550448000/1550707200

20

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4) Stormy Storm Field Practice (23)

https://backpack.tf/profiles/76561198074424269#!/compare/1549929600/1550275200

https://backpack.tf/profiles/76561198092541990#!/compare/1533859200/1550275200

Practice sold with 3 keys for Disco Beat Down Snowcapped (26)

https://backpack.tf/profiles/76561198074424269#!/compare/1548633600/1548720000

https://backpack.tf/profiles/76561198302291309#!/compare/1548633600/1548720000

Snowcapped

https://backpack.tf/suggestion/5c58743b44325a71f15a9cb2

26 - 3 = 23

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https://marketplace.tf/items/147;5;u63

5) $41 on December 25th, keys were $1.8

41/1.8 ≈ 23 keys

6) $41 on December 31st, keys were $1.76

41/1.76 ≈ 23 keys

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Total: 20, 20, 22, 23, 23, 23

If you will find other sales, you're welcome to report them.