ContainerBoy:
Just a quick one Dave
Oh dear, this isn’t going to be quick. 
ContainerBoy:
but do you have to do Core first?
Yes, you have to do Core, then either Packages OR tanks AND at least one Class.
I wrote this earlier, but I should have written… all on the same course.
Then you get an ADR card. 
ContainerBoy:
Can they be taken in any order?
No, but once you’ve got a valid ADR card, you can add anything else at a later date and in any order you like, but see above because you need the card first before you go adding other bits to it.
ContainerBoy:
I gather that if someone did Core then either Packages and/or Tanks but decided to do two or more Classes at a later date then the moment you do one Class they will issue you with certificate or card.
Yes, that’s sort of nearly correct. You need Core PLUS either Packages OR tanks PLUS at least one Class.
After that, each time you do any ‘additional(s)’ they will issue you with a new card if you pass the relevant exam(s.)
If you take and pass two Classes on the same course at a later date, you’ll be issued with a new card that has both of your new Classes on it.
I can’t imagine why anybody would even think of going to all that trouble though, because they’d be taking chunks out of several different weeks and lose far more in terms of lost time/wages.
It would also take quite a while to get a ‘full set’ by this method, because (usually) even a fairly prolific ADR provider only runs one ADR course per month.
ContainerBoy:
But if you havn’t finished and are still going to get around to doing another Class then they would need to issue it again with the updated classe(s).
See last answer.
ContainerBoy:
So if you did Core last (when you know you’ve finished doing the moudles you want then and only then would it trigger the issue of cert/card.
Sorry mate, please see my first answer. You can’t do Core last.
It seems that you might (possibly) be massively overthinking this and tying yourself up in knots in the process, it’s quite straightforward really and far less complicated that you seem to think.
Please don’t let this worry you.
Once it’s time, you can ask again just in case the rules change in the meantime.
My best tip is that you get your MOD 4 in the bag and on the system before you consider any ADR course.