I’d love more info on that too. All we know for sure is that there was also number 17, and the 48s. The 48s were the next series after 47, so it’s very possible that 17 was a lower series than 47, though I always assumed he was part of series 4 as well.
The novels give a little more info, but I don’t trust them as canon as IO have never confirmed them as such.
Based on canon, there must have been five series, as 47 was a part of series 4, and Ort-Meyer made the 48s directly after him which would make them series 5. We can assume that most of the earlier series of clones were harvested for their organs due to the information in C47.