Need to create a custom column for New customer using group by and IF ELSE statement.|Power Query|Excel Forum|My Online Training Hub

Continuing some more details on my original post.
While my post was getting verified, I did some research and performed these two queries to achieve the two custom columns I have mentioned above.

Steps I followed

1. Uploaded data into Power Query
2. I referenced my orginal PQTest query which I loaded to PQ.
3. then wrote the below in advanced editor:
   let
   Source = PQTest,
   Custom1 = Table.Group(RawData_iDigSales,"Account-Zip-Sku",{{"Sku Count", each if [Invoice Dates] = [Start of Month] then "0" else "1"}})
   in
   Custom1

From the above Helper Query I derived  a partial or incorrect Sku Count.

This is where I hit the road block : I wanted to use the query 

let
Source = PQTest,
Custom1 = Table.Group(RawData_iDigSales,"Account-Zip-Sku",{{"Sku Count", each if [Invoice Dates] <= [Start of Month] then "0" else "1"}})
in
Custom1

But PQ threw an error as below when I include "<=" expression in the query.

Expression.Error: We cannot apply operator <= to types List and List.
Details:
Operator=<=
Left=[List]
Right=[List]
The above is Problem number 1
Yet I continued becuase I am hoping to find the solution to problem number 1.

      4. Then I merged the above helper query with the PQ Test query as a new table called it Merge 1

      5. Using the Merge 1, I referenced the query to derive the next custom column ="New Account"

      6. Used the below query in advanced editor:

let
_reference_date = #date(2021,01,01),
Source = Merge1,
// #"Changed Type" = Table.TransformColumnTypes(Source,{{"Sku Count", Int64.Type}})
Custom1 = Table.Group(Source,"Account-Zip-Sku",{{"New Account",each if List.Min([Sku Count]) = 0 and List.Min([Invoice Date]) >= _reference_date then "Y" else"N"}})
in
Custom1

Now my request to all is, is there a way to fix the "<=" expression error and is there a more agile way to derive these custom columns instead of the long process I have here?

Note: Although I am grouping, I still need to retain all rows from the orginal table.

Thank you for reading and your help.