From what I have seen these processes are followed pretty closely in terms of project management. What does not always stay consistent is the difficulty of the processes and how long they will take, particularly in the execution phase. Many times, issues arise in the execution stage where an expected process that was thought to be easy or have no problem is actually not possible.This would require remediation plans or a strategy that solves the problem. Other times, a wrench just gets thrown in the whole process, stalling out the project for unavoidable reasons. I’ve worked on a project before where a change to a product was being made, but then it got stalled out because another project was making changes already to it before we could, meaning we would have to wait until they were done updating it (they took months!).