Thanks Bob,
Headway has been made.
However, using
IIf([TypeDay]<>"HOL",[CalDate],DMax("[CalDate]","Tbl_CalDay","TypeDay <> 'HOL' AND CalDate < #" & [CalDate] & "#"))
Gets the message "#Error" on the Holiday, instead of the last valid MDay that I need.
I reversed it a bit and got it to...