Harlan wrote...
The weeks, 1-4 are in row 2 in the Weekly Worksheet. *So yes, there are 4
columns for the weeks, going from C2:BF2. . . .

C2:BF2 is 56 columns. If there are 4 weeks per period, then there'd be
56/4 = 14 periods. You had said previously there were 13 periods. I
can see how having weeks begin on Sunday or Monday and years beginning
on 1 Jan and ending on 31 Dec you could have 53 weeks, but I'm at a
loss to figure out how you have 56 weeks.

. . . What I don't understand in your formula are the curly brackets. . .