As azumi said, it is not a good idea to have merged cells in the sheet if they are being referenced in any formula in the sheet.
So I have removed the merged cells from Summary to March sheets. You need to remove them for the rest of the sheets.
Then on summary sheet in B6, try this........
=IF(INDEX(OFFSET(INDIRECT($A$2&"!D$11:D$40"),COLUMNS(B$6:B6)-1,COLUMNS($B6:B6)-1),ROWS(B$6:B6))=0,"",INDEX(OFFSET(INDIRECT($A$2&"!D$11:D$40"),COLUMNS(B$6:B6)-1,COLUMNS($B6:B6)-1),ROWS(B$6:B6)))
then drag across and down.
For detail see the attached sheet.
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