To answer your question, I would think the diy versions of their flavors will most likely yield the same results as their premix. They must know the percentage they use and then recommend the same for the DIY version.
With that being said, they are selling their recipe as the flavoring alone. If you use an inferior base to what they use or an inferior nicotine solution, then your result may not be as accurate.
My ADV for quite awhile was the same as yours, loved it. Started to fully DIY about 6 months ago now. I have a recipe that is very close that I still
vape now and again. My tastes have moved over to cheese cake variants now over custards lately.