1 toilet overflows ............ your choice, Bambi. It would depend on the floor covering. With bare floorboards, it could drip through a gap between boards, and not show very much at all until the damp patch spreads out.
With a vinyl covering, it could pool. If you'd like it to, a Victorian floor could easily not be level. Water could run across the vinyl to anywhere you like, and not be discovered for a while.
2 Pipe dislodged. Entirely up to your timescale. Yes, plumber eventually, but the leak, even after disturbing, could be as much or as little as you need. Helpful C could pull the pipe apart completely, then flood, then plumber.
3 Yes, holding up ballcock could stop the incoming flow if the valve simply wasn't seating properly......... or, it could have become completely defective, where it would not stop the flow whatever you did to it. Both are perfectly feasible.