^^^ you are probably right about pseudo being left if not enough I2 was provided to make HI. I just always assume HI is pre-made and some kind of phos compound is used as a recycling agent. In this case, all pseudo is more than likelly to first be transformed into iodo-pseudo or iodo-meth if you like before a further reduction takes place.
As for the Birch you speak of, the stuff can't really have anything other than meth and unreacted pseudo in it. The pseudo has a characteristic taste when smoked of course, so its easy to tell if its present. I am sure the incident you refer to happened a fair while ago. The lore now is that pills are so gakked up that a fairly in depth extraction is needed. In the old days, some people report, all that was needed was a bucket of ammonia, chuck sodium in, chuck crushed pills in untill blue goes away and wait for meth oil to float to the top. This of course would no longer work, so I am by no means providing any recipes here. Also, must be noted... what cook would ever give out secrets.
These days, when I get a chance to smoke some good meth, (and that's not often - perth drought), I always assume its imported from Asia.