It is true that all reactions should be cleaned up afterwards. And shit in = shit out, no matter which way you wanna reduce it. (So clean ephedrine is better, with less impurities to be reduced)
Something that I have found however, is that NONE of the articles I have read about performing birch reactions discuss over reduction, which is highly possible - considering that none of them give a method for weighing Lithium/sodium/alkali metal to the accuracy required (not easy to weigh something that is so reactive). You put in too much lithium (or whatever metal u choose), you'll end up with di-meth.
It seems to me that perhaps it would be better to add just a bit too little - end up with some unreduced ephedrine - and seperate the mix?

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Something that I have found however, is that NONE of the articles I have read about performing birch reactions discuss over reduction, which is highly possible - considering that none of them give a method for weighing Lithium/sodium/alkali metal to the accuracy required (not easy to weigh something that is so reactive). You put in too much lithium (or whatever metal u choose), you'll end up with di-meth.

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Forgive and correct me if I'm wrong, but:
How would adding too much lithium thus over-reducing take methamphetamine -> dimethamphetamine? Mustn't it be some other pathway if possible at all, since methamphetamine to dimethamphetamine is not reduction but alkylation?

Essentially- What the fuck are you talking about?