RC yield meaning recrystallization? Well unless you had a control test before it was stored to see how much a re-x on the 'clean' dmt before the oxidation yields, you dont really know how much of the loss was actually because of what you suppose its dmt n-oxide and what were other impurities or even dmt loss (there's always some dmt in the goo that stays on the bottom of re-x )
I have witnessed dmt changing colors with storage in impropper conditions but I've personally found it to be equally active using an effective vaporization method. It is possible the oxidation is mostly superficial and that a lot of DMT is still intact. It may also be that the darkening is not happening to dmt but to other impurities in it (or to both), for example dmt has been shown to also have traces of NMT when extracting from mimosa (and some acacias), and NMT darkens color and yet does not form oxides (I think its not known what causes the darkening?).
Some people feel DMT n-oxide is qualitatively different than DMT (some say mellower, some say darker, some say lighter, some say harsh, etc) but this may also be due to self suggestion, or also smoking method and the differences in vaporization efficiency of an oily product vs a crystal one.
There have been few if any double blind tests to say if people can really notice a difference, if its there. In any case just dont throw anything away, bioassay separately if you want. It's possible pharmacologically DMT N-oxide metabolizes into DMT
Also sometimes people talk about yellow=n-oxide but there is not much evidence that confirms that. DMT N-Oxide is very easy to tell appart from DMT in TLC, and I havent seen anybody showing n-oxide in these extractions. I've neither found evidence of n-oxide in yellow dmt with TLC, but that doesnt mean its not possible. The ideal would be to have some DMT test it before with TLC or other analytical equipment if available, and then after a certain time test again stored in good conditions vs in bad conditions.