“That is not license to make up stuff and pass it off as truth.”
I don’t believe that one needs “make up” your reliance on sola scriptura.
We are told that if anyone teaches other than what the apostles taught we were to consider them accursed.
Galatians 1:8 But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed.
Please find for us an infallible source for the teaching of the assumption of Mary. If you can't find any other infallible source for what the apostles taught we will stay with Sola Scriptura as our base guide for truth.