3 In-date Marketplace.tf sales https://marketplace.tf/items/tf2/30922;5;u3025

June 1 2020: $55.56 (Median key price: $1.92, 55.56/1.92=28.94 keys) ~29 keys (untraceable via item histories)

July 14 2020: $54 (Median key price: $1.93, 54/1.93=27.98 keys) ~28 keys (look below)

July 18 2020: $55.56(Median key price: $2, 55.56/2=27.78 keys) ~28 keys (look below)

https://bot.tf/stats/listings/MQ01QGV1 The seller at 28 keys on Backpack.tf has listed their one at 28 keys on July 5 2020 and is still unsold, we can safely say 29 keys is the outlier

https://backpack.tf/item/6644924232

https://backpack.tf/profiles/76561198063054044#!/compare/1594684800/1596067200

This shows one of the taunts going into the Marketplace.tf buyer's inventory between July 14 and July 30 (there's a gap because Backpack.tf has been down) so this must be the item history for either the sale on July 14 or July 18, the other is untraceable

The sale on June 1 is untraceable too

Going with 28 keys