Hope you can all excuse my terrible unusual suggesting skills. Here we go.

Going back to August at max.

https://marketplace.tf/items/30609;5;u3006 - 5 sales

Sep 16: 1x $20.99 - http://manic.tf/keyprice/?at=2018-09-16 ($20.99 / $1.85 = 11.35 keys)

Aug 27: 2x $22.22 - http://manic.tf/keyprice/?at=2018-08-27 ($22.22 / $1.89 = 11.76 keys)

Aug 13: 1x $16.99 - http://manic.tf/keyprice/?at=2018-08-13 ($16.99 / $1.88 = 9.04 keys)

Aug 11: 1x $21.99 - http://manic.tf/keyprice/?at=2018-08-11 ($21.99 / $1.87 = 11.76 keys)

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https://bot.tf/stats/item?def=30609&q=5&ef=Screaming+Tiger&craft=1&aus=0&ks=0 - 4 sales

Sold:

Aug 26: 9 keys, 26 ref

Seller: https://backpack.tf/profiles/76561198305676157#!/compare/1535155200/1535241600

We have a perfect trade, but no constant buyer username. https://gyazo.com/182ed7bd1d0e9894f23ddc2aacc8a53f

The person who currently has it has almost never had their backpack archived, which may explain it: https://backpack.tf/u/76561198422644188

They bought another one, too. https://backpack.tf/item/6502529942

https://backpack.tf/profiles/76561198274288711#!/compare/1535241600/1535414400 - looks like 10 keys, but same shortcomings

Sep 21: 9 keys

Seller: https://backpack.tf/profiles/76561198334598690#!/compare/1537315200/1537401600

Buyer: https://backpack.tf/profiles/76561198334946156#!/compare/1537315200/1537401600

Found 4 keys:

https://backpack.tf/item/6549040226

https://backpack.tf/item/7067732988

https://backpack.tf/item/7091478845

https://backpack.tf/item/4241045333

Bought: Considered quicksells. Not using.

Aug 17: 5 keys, 12 ref

Sep 4: 5 keys, 20.44 ref

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We've got sales at 9 and what rounds to 12, so there's our range :)