It is helpful to appreciate that for most of the columns, you are answering a yes/no question, where tick means `yes', cross means `no', and ``E'' means `no but excused'.
A tick (or even a cross) is interpreted as a hyphen if the student has a tick in the previous column (completed by the deadline), so you don't need to worry about scribbling out a tick if the student unexpectedly manages to complete in time.
A student may not be given the extension, nor an excuse for not having asked for the extension, if they have a cross in the attendance column. So, if an absent student retrospectively wants the extension, he or she must first explain the absence! If you accept (and record) this excuse for being absent, the student is automatically given the extension.
Whenever you accept work for marking from the student you must always put an entry in one of the `Completed by [session date and time]', `Completed by [extension date and time]', or `Or completion date' columns as appropriate. This must be done immediately, even if the work is actually going to be marked some time later.
If a student comes to you and argues that his or her work should not be flagged late, and you agree, there is no point simply crossing out the Late flag: you must fix the cause of it.