This time I've got it right...

SCM MannCo Keys at time of purchase 2.44 (Feb. 7th, @3PM):

https://steamcommunity.com/market/listings/440/Mann%20Co.%20Supply%20Crate%20Key

SCM Purchase 46.96/2.44 = 19.2 keys = ~19 keys

Proof provided by seller:

https://steamuserimages-a.akamaihd.net/ugc/1762567744324033327/932A65AFF08E04C9F8C446255E233E539877F514/

Looking through the backpack comparison is a mess, but all I could be certain of is it was also listed on SCM between 2019-10-17 and 2020-11-14, and the only recording sell order that fits the time frame is unfortunately too old to be reliable, as is the case with any previous trades.

Let me know how I did :)