The first thing to do is deal with your last question, because it applies to all of your queries. The term ‘Completion’ in the ECC is a defined term because it has a capital initial – see clause 11.1. The definition is in clause 11.2(2). This should remove the subjectivity involved in similar terms found in other contracts. Note the definition enables you to define exactly what you mean by completion as part of your works information.
In addition, it is important to understand that, unlike other contracts, completion is purely about what state the works are in. The term ‘take over’ is used to describe who is using the works – see clause 35 for that. Take over can occur before, at the same time as, or after completion, depending upon the circumstances set out in clause 35.
If you have used option X5, then a certificate of completion is required to be issued for each section of the works. Note that this certificate must be issued by the project manager within one week of the date that each sectional completion was achieved – see clause 30.2. As such they all need to be issued separately. The same comments apply to the take over of each section, which also has to be certified by the project manager within one week of it occurring – see clause 35.3.
Finally, half of the retention is only released when completion or take over, whichever is sooner, of the whole of the works occurs – see the first line of clause X5.1 and use of the words, ‘the whole of the works’ in clause 16.1. No retention is released for sectional completions or sectional take overs.