It sounds like there are many parts to your question !!
I am not sure what procedure you are following, but any compensation event notified by the Project Manager, or notified by the Contractor and accepted by the Project Manager, becomes part of the scope of works.
In response to your questions;
I am not sure what Part 3 is, but I am guessing that it is a notified (and accepted) compensation event. The Project Manager should notify a further compensation event to rescind (remove from the scope of works) the first one…
Where Others have undertaken the work then the Project Manager should again notify a further compensation event to rescind the first one.
Again the Project Manager should notify a further compensation event to rescind the first one.
Note that there may be an element of Defined Cost associated with any of the above sceanarios which should be included in a corresponding quotation assessment.
This assumes that none of the above relates to a ‘proposed’ compensation event, in which case the Project Manager should notify that the matters will not be formally instructed.