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Spirulina and tempeh contain mostly analogues of B-12. Herbert [1988] reports that tests on tempeh, a fermented soy product, and spirulina revealed that they contained almost no true B-12, i.e., the "B-12" they contained (per USP assay test) was predominantly analogues. Herbert [1988, p. 857] reports:
We suspect that people taking spirulina as a source of vitamin B-12 may get vitamin B-12 deficiency quicker because the analogues in the product block human mammalian cell metabolism in culture [i.e., in the lab] and we suspect that they will also do this in the living human.
The presence of analogues, rather than true B-12, in fermented foods makes them unreliable sources for B-12.