Sum columns where date appears on column heading

[Mingeita]

Hi,

I have a parts spreadsheet which shows parts and required quantity.
Each time there is a shipment, a new column is appended with the heading "Shipped ##.##.####" where ##.##.#### is the date of the shipment.

I need to be able to sum shipments for each of these parts, but only where the month of the date in the heading is April (4).
Is there any way to do this please?

I've attached an example file.

[AliGW]

Get rid of "Shipped by" - instead, have another row above the dates that says that and have just dates in the header row, then this is easy with SUMIFS:

=SUMIFS($D3:$I3,$D$2:$I$2,">="&DATE(2021,4,1),$D$2:$I$2,"<="&EOMONTH(DATE(2021,4,1),0))

[Mingeita]

Great. Thank you.

[AliGW]

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