I can confirm what Gerhard Popp said, having been myself, involved in the work on green spectral sensitization and coating of negative films. Although he was not head of that division when I was in it, we were working with that problem many years ago and found it to be quite correctable without an extra layer.

However, some Kodak films did have what was essentially an extra layer in the sense that the fast and slow components of the C and M layer were coated in separate operations to improve speed and grain.

Fuji was constrained from some of these approaches due to existing Kodak and Agfa patents.