Hello, apologies if I sound completely clueless - I am 
My plan at the moment is to sit the SAT I in October, sit the two subject tests in November and submit these scores to JHU (Early Decision) by Nov 2.
However, as these will be my first SAT exams I am not confident I will achieve my desired scores - so my plan is to retake the SAT I in December and submit this to all my other colleges for regular decision by Jan.
I was just wondering, would it be possible to do this? submit different scores to my ED and RD colleges and apply to them at different times? Sorry if this is a ridiculous question, but I have no idea how the common app system works.
And do you think it will be okay to only take the SAT once (for my ED)? I missed the deadline for the June exam and they don’t have a waitlist system in my country - the next available date is October
thank you for your help everyone!
Absolutely. You should submit better score to any school before the decision is made. Nevertheless, you are a bit behind schedule. If you want to apply to some schools in EA/ED, you should have your first score at least before Summer so that you can maximize your chance by picking more reasonable schools on the list. Also, don’t wait for December to retake the SAT1 even for RD. Get yourself well prepared for the test over the summer and take it in early Fall before you are overwhelmed with school mid-terms and final exams. Ideally, you should have your final SAT1/ACT scores by October (or June, if possible).
It is hard to say whether it is okay if your only take the test once. You should treat each attempt as your final attempt anyway. If you do practice thoroughly and get the score similar to your plateaued practice score, that should be it. It would be a bad idea to apply to any school blindly even without a score on hand though.