How to reference another filtered table with a related field Power Query (M)

See the working here - Open a blank query - Home - Advanced Editor - Remove everything from there and paste the below code to test

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WMjIwtNQ1MFTSAbIMlGJ1YCJGQBFjFBFjoIgJSCQWAA==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"YYYY-WW" = _t, #"Units Sold" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Units Sold", Int64.Type}}),
    #"Added Custom" = Table.AddColumn(#"Changed Type", "Week Start Date", each List.Min(Table.SelectRows(Calendar, (x)=> x[#"YYYY-WW"]=[#"YYYY-WW"] )[Date]))
in
    #"Added Custom"

 Code for Calendar

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("bc89CsMwDIbhu3hOsSXnx75At04JZAgZCg20Swulvn9MW4mAvkUgPWh4l8UR+xg8B0qucWN51lmXfArk1ubHJHx5GfZfzPU8lc0gC87bzWDUz3sx2Aqe3w+DneB4/RjsFQ8x/MdB8JgimFCKYEYpghRQiyqhGFVGNaoR5UTRFvWodihItUdFqgMqUk2oSDWjoqrrDg==", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Date = _t, Day = _t, #"YYYY-WW" = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Date", type date}})
in
    #"Changed Type"