Lock 91

There are 91 locks on the Rochdale Canal, this is the penultimate lock, Lock 91. Lock 92 is at the junction with the Bridgewater Canal at Castlefield Basin.

How is Lock 91 the Penultimate lock on a canal with 91 Locks?, when the canal was restored, locks 3 and 4 were combined into a single deep lock (numbered 3/4).