Calculated column that repeats a season by docnr.

[Pivvv]

Below I have a screenshot of all documentnumbers but in the column Season I only get the season in one of the Documentlines.
I am now trying to create a calculated column that repeats the season for each line of a docnr.
I'm feeling that I have to use the function EARLIER but I can't get it to work.

The endresult should be the green column. This is pretty easy with Excelformulas but not so easy in DAX
I'm trying for 2 hours now but maybe I should start reading a book instead of using google + trial and error Altough I learned a lot in the meantime!
Does somebody knows a way out?

 

[Ozeroth]

This looks like something you should fix in your table before importing to PowerPivot (e.g. with Power Query), and it might make sense to have a separate lookup table with just Docnr & Season...

...but, to do it with DAX as a calculated column in your existing table, I would probably do it this way:

=CALCULATE (
    IF ( HASONEVALUE ( Table1[Season] ), VALUES ( Table1[Season] ) ),
    ALLEXCEPT ( Table1, Table1[Docnr] ),
    Table1[Season] <> "NA"
)