This is an excellent topic subject to a wide response from many groups outside of the control system world. I wonder if any standards define these terms. I regard these as subjective terms unless the client has a definition in the contract - or contractor defined the terms in the bid. This is a not a big issue for a small project that requires two-months from construction completion to startup. The terminology is a bigger issue for a large project that may require over a year to test and commission.
Where does commissioning end and startup begin? Does commissioning include the first fills? For a gas-turbine compressor commissioning might include running the turbine with driven equipment uncoupled. Is the initial equipment startup with the compressor coupled and moving gas for surge testing part of commissioning or startup?
Let's hit the common items of easy agreement, expand the list to include a variety of activities and table which each regard as construction, hookup, pre-commissioning, commissioning, maintenance, preservation, startup, etc. We need to operate some utility systems to perform much of the completion work. Is there differentiation between the utility systems and process systems?
Construction should be complete for systems or subsystems before any testing begins. There should be commissioning procedures to define the various steps. Inspection Test Records should be recorded in a database to track the construction completion status.
If we commission an instrument system to soon there may be other activities that undo our work. Some examples include the reinstatement after flushing, chemical cleaning, helium leak detection, etc. If we break something that was commissioned and replace it, what is the status of the various QA test records?
Consider preparing a table with the activities, your definition among the completion or commissioning status then invite a vote.