Auto-Fill Problem

Why won't Excel recognize this pattern as I drag it down the column with Autofill?

L26 cell has =SUM(Sheet1!$C1:$BB7)
L27 cell has =SUM(Sheet1!$C8:$BB14)
L28 cell has =SUM(Sheet1!$C15:$BB21)

But when I highlight these cells and click Autofill in the bottom right, it returns this in cell L29:

L29 cell returns =SUM(Sheet1!$C4:$BB10)

Any help would be greatly appreciated.

Thanks in advance.

I am new to this forum. I apologize if I am doing something wrong. I asked a similar question last week and got over 100 views without garnering a response. Could someone please let me know if I am doing something wrong i.e. viewers can't respond, bad ettiquete, etc.

Thank you so much for answering. I am still very much a beginner. In effect, how would that apply to:

D17 =SUM(Sheet1!$C6:$BB12)
D18 =SUM(Sheet1!$C13:$BB19)
D19 =SUM(Sheet1!$C20:$BB26)

then D20 returns =SUM(Sheet1!$C9:$BB15) when I autofill.
Sorry about the multiple questions, I am right on the cusp of comprehending this. I appreciate both of your responses

Hm, I tried to make an adjustment by filling in the information to meet the criteria for my second question, but it is returning the wrong answer. Here is the formula I used:

=SUM(INDIRECT("Sheet1!$C" & (ROW(D17)-17)*7+1 &" :$BB"& (ROW(D17)-17)*7+7))

Is there an error in this?