It sounds like the OP is misunderstanding the referral deal, or am I? You give your friends a referral code and THEY must order before Sept 16th to get free super charging, and they must order an S, X, or M3P to get it. Doesn't matter when or which one you order, right?
That was my understanding.
I buy a Tesla, I get a referral code that I can give to my friends. I can supply this verbally, as an internet link or written on a piece of paper for them to quote to a salesperson if necessary so they can buy a Tesla & get free unlimited supercharging.
A referral code is for life [Tesla ownership] not just a time period.
If my friends want a Tesla with free unlimited supercharging they have to buy a S, X or M3P using my code before Sept 16th, after which point I'm not sure what the referral program will offer.
If they order a Tesla they will get their own referral code ... and so it goes on
When they order has no bearing on my order or on my referral code just on what they receive as the person being referred.
Separately, if I fiddle with my order such as changing car colour etc, before the order is locked in then that also has no bearing on my referral code or my ability to supply it.
Although I'll caveat all this with the fact that I bought an S & you can't currently buy a M3 in the UK so I have no idea what a Tesla account looks like if you become a Tesla owner by buying a M3 & don't own any other Tesla cars.
Until my car was delivered I didn't have app access (got the same message as above) but I've always had a My Tesla account as that's what I ordered through and that has always looked like this below, from the day I created the account I have had a referral link. I just emailed folks the link