=SUM(C3:INDEX(B9:C11,2,2)) adds C3:C10, but only C3 and B9:C11 were
recorded as its precedents, so typing into C5 left the total unchanged
until a full recalculation. A range whose ends are function results now
depends on the box spanned by the references inside it, which contains
any cell those functions can return.
Typing a value over a dynamic array formula, or clearing it, left the
values it had spilled: with =SEQUENCE(3) in A1, typing 2 into A1 kept
2 and 3 in A2:A3, and =SUM(A1:A3) gave 7. Only formulas are evaluated
again, so the old spill of a cell that no longer holds a formula was
never written back. It is now removed when the formula goes, and the
formulas reading its area are recalculated.
nihilist-narwhal