Sum different # cells

Mabe this will get the ball rolling

Using two helper columns (A:B), these can be hidden.
In A4

=ROW()

In A5

=IF(C4="",ROW(),"")

Drag/Fill Down until the last row of your tables plus two more rows.

In B4

=IF(A4="","",IF(MIN(A5:$A$1000)>0,MIN(A5:$A$1000)-2,MIN(A5:$A$1000)))

Drag/Fill Down as above.

Then in D4

=IF(C4="","",COUNTIF(INDIRECT("C"&MAX($A$4:$A4)&":C"&MAX($B$4:$B4)),C4))

Drag/Fill Down

Can you get what you need from that?