Resuggesting: https://backpack.tf/suggestion/5e8c9b59fca58a603933701e#comment-5ea0df88032d30338e652959

MP sales:

https://marketplace.tf/items/tf2/538;5;u12

Jan 19: 36.99 / 1.77 = 21

$35.32, April 8th, can't find the histories

https://manic.tf/keyprice/?at=2020-04-08&price=35.32 - $35.32 / $1.69 = 20.90 keys

Bot.tf sales:

https://bot.tf/stats/item?def=538&q=5&ef=Massed+Flies&craft=1&aus=0&ks=0

1 @ 22 keys 10/02/2020 https://backpack.tf/profiles/76561197990037025#!/compare/1581206400/1581292800

1 @ 20 keys 07/03/2020 https://backpack.tf/profiles/76561198358965606#!/compare/1583535600/1583622000

Other trades:

1. https://backpack.tf/item/4995988167

https://backpack.tf/profiles/76561198253383258#!/compare/1581638400/1586217600

Unusable

2. https://backpack.tf/profiles/76561198341171690#!/compare/1586217600/1586304000

https://backpack.tf/profiles/76561198176022675#!/compare/1586217600/1586304000

https://backpack.tf/item/8059188120

most likely 19 keys + 19 ref

https://i.imgur.com/3XObT92.png - labelled as that here. sold to a gambler, looks like. histories don't match (probs because it was gambled before being scanned in their backpack), but we can see exactly 19 keys and 19 ref on the seller's end so this should be fine to use.

3. https://backpack.tf/profiles/76561198799983169#!/compare/1586476800/1586563200

https://backpack.tf/profiles/76561198850274253#!/compare/1586476800/1586563200

untraceable

Taking 19 - 21

Big thanks to Jarool for the help