Tbf it is always stated as a minimum of extra time added, the annoyance is that refs often seem to be inconsistent in whether they add any extra on again and what for.
Tbh having the timing done separately would make things an awful lot clearer and take away any suggestion of corruption - might also mean that we'd get 90mins of playing time as iirc it only averages out at 70 odd.
Even the minimum 7 minutes put up by the 4th official was questionable.