#+TBLFM: @6$2=vsum(@II+1$2..@III-1$2)::@7$2=@1$2+@2$2-@III+1
Take a look at Bastien's tutorial about table calculations in Org:
In order to make sure that the formula stays correct, you need to
make sure that you add more lines to the table only with the
proper command M-S-<down>. When using this command, the absolute
references in the formulas are modified.
I can see that a construct like you have been using would be
useful, because it would allow normal editing of the table and still
keep the correct results. I have taken a note, maybe this
can be implemented at some point.
HTH
- Carsten