Dinamically Return Values From a Column Using A Merged Header Above It as Conditional

Calheiro 

An advantage of using 365 is that array shaping functions are available to use as part of the calculation.  For example the following generates an array containing the CS+IN columns only, each with the appropriate date header.

= LET(
    dateHdr, TAKE(WRAPCOLS(date, 5),1),
    wrapped, WRAPROWS(TOCOL(stock),5),
    CS,      WRAPROWS(TAKE(wrapped,, -1), COUNT(date)),
    XLOOKUP(csMonth, dateHdr, CS)
  )

From there, lookups should be simple.  Whilst developing the formula the intermediate variables can be output to scratch space as helper ranges but, once everything is up and going, these can be removed.