New at Ancestry, Worcestershire, England, Electoral Registers, 1837-1974 has 7,306,656 records. Electorial registers are great for helping bridge gaps between censuses.
The bar chart shows the major increase when women got the vote. The other variation likely just reflects the availability of registers.
The index, created using text recognition software, is subject to error. In searching the name Northwood I found four instances in 50 with the continuation of an entry to a second line not recognized and a separate record added. There never was a person Northwood Halt! Always check the linked image of the original.
You will also find cases where a business address is given — not a different person — just a separate entry from that for a home address that may not be in the county.
The originals are from the Worcestershire Archive and Archaeology Service.