No, the 9918 can take 20 cells as well. it's the very same controller, only using a different label. The only thing changed over time is the BEC; for use on lower voltages (such as 6 cells)
One other thing to note is.....this
warrior series controller's have amp designation first...examples 9920, 12020
while the Micro series controllers have the cell designation first...
example....2095, 20120