I'm not in Medical at all, so read this with that knowledge in case it makes a difference.
You do stuff (a process- rev A)
At some point the process must be changed for a valid reason (a process - rev B) {Day 10}
...but you're not sure rev B process works...
So you try it {Day 15}, and test it {Day 25}, and tweak it {Day 50}, and validate it {Day 75} until you have a process that works again.
Now you have to update your document, and do so {Day 85}
...and it gets approved... {Day 100}
...and distributed for use {Day 101}
Which day did you start "using the process" ? Pretty much Day 50
When did you confirm it was the right process to be using? Pretty much Day 75
When did you document it? Pretty much Day 85
When was the doc approved? Day 100
When was the approved document distributed for use? Day 101
Which one is the "effective date"?
If it is de-facto Day 100...what did you do with the stuff made by that exact same process earlier than that?
The document is "effective" when people have the ability to follow the approved document...Day 101.
The use of the process documented started Day 50.
The use of the documented process started on Day 101.
I guess the real question here is whether the documentation follows the process, or vice versa. Chicken and Egg-ish.
If I ran 5 days production as a final validation before locking it down in the approved doc...do I really have to scrap it all, after following the exact same process in all respects, just because the Document de-facto effective date is later?