How did unidentified narrators make their way into Shia books? How is it possible for fabricated hadiths from unknown narrators to be included in Shia books despite the scarce but true followers of the Imams?
Just because a hadith has an unknown narrator does not mean for certain it was fabricated. Possibly the narrator was known in the past, but we do not know them now because we have lost books and information. Also, possibly the information in the hadith is correctly transmitted even if we don't know the transmitter. It is better to say that hadith with unknown narrators lack verification.