Adding/merging a Custom Column based upon a Date Condition

Hi CincyKJ, another solution:

Output

let
    TableTransactions = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("TcnBCcBACETRXjwvOGrGmFrE/tvIEggs/H963ZJMPnXJEvuHIhQps1o8gjf9YFB3Zh8bmFl1cunOITMv", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [#"Transaction #" = _t, Location = _t, #"Rate Class" = _t, #"Transaction Date" = _t]),
    TableRates = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("bc5BCsAgDETRu7gWJqOJtmcR73+NRkuhBBdC4PNMxkhMeT+pEELUxyqSZv6ljlWbjxoSZat7JQtKUS5QDsp/KwrypHxXeZNF5cTAtcuian4eipxUB/0Sfmo+", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type nullable text) meta [Serialized.Text = true]) in type table [Location = _t, #"Rate Class" = _t, #"Rate Effective Date" = _t, #"Rate Amount" = _t]),
    ChangedTypeTransactions = Table.TransformColumnTypes(TableTransactions,{{"Transaction Date", type date}, {"Transaction #", Int64.Type}, {"Location", Int64.Type}, {"Rate Class", Int64.Type}}, "en-US"),
    ChangedTypeRates = Table.TransformColumnTypes(TableRates,{{"Location", Int64.Type}, {"Rate Class", Int64.Type}, {"Rate Effective Date", type date}, {"Rate Amount", type number}}, "en-US"),
    StepBack = ChangedTypeTransactions,
    MergedQueries = Table.NestedJoin(StepBack, {"Location", "Rate Class"}, ChangedTypeRates, {"Location", "Rate Class"}, "Rates", JoinKind.LeftOuter),
    Ad_RateAmount = Table.AddColumn(MergedQueries, "Rate Amount", each Table.Max(Table.SelectRows([Rates], (x)=> x[Rate Effective Date] <= [Transaction Date]), {"Rate Effective Date"})[Rate Amount], type number),
    RemovedColumns = Table.RemoveColumns(Ad_RateAmount,{"Rates"})
in
    RemovedColumns