Sale 1:

https://backpack.tf/profiles/76561198341171690#!/compare/1588982400/1589068800

https://backpack.tf/profiles/76561198081865826#!/compare/1588982400/1590364800

= 10 Keys.

Sale 2:

https://backpack.tf/profiles/76561198043936328#!/compare/1592438400/1592524800

https://backpack.tf/profiles/76561198037944582#!/compare/1592438400/1594252800

Untrace / Bulk.

Marketplace.tf: https://marketplace.tf/items/tf2/31025;5;u33

Sale 3:

May 13 - $18 / $1.90 = 9.47 keys, No B/O

= 9.5 Keys.

Sale 4:

Jun 15 - $12 / $1.99 = 6.03 keys, No B/O

= 6 keys, QS

Sale 5:

Jun 17 - $24.99 / $1.98 = 12.62 keys, No B/O

= 13 Keys.

Sale 6:

Jun 17 - $13.31 / $1.98 = 6.72 keys, No B/O

= 6.5 Keys, QS

Sale 7:

Jun 29 - $24.99 / $2.01 = 12.43 keys, No B/O

= 12 Keys.

Sales: 6, 6.5, 9.5, 10, 12, 13

Going with 9.5-13 keys.