If you are producing nice white crystals, you're probably getting >95% DMT. With a mimosa extract, it is easy to achieve this. If you are extracting from acacia confusa, most crude extracts contain about 50/50 DMT/NMT. However, with
good methods you can get high purity DMT from either source. With enough recrystalizations, the purity will approach 100%.
In theory, you should be able to isolate 100% DMT from either natural or synthetic source if you purify it enough. If someone were to synthesize DMT, they would still have to purify it using conventional techniques (i.e. recrystalization), so it's really just down to whether the contaminants are natural or byproducts of a synthesis reaction.