Back in February, this collection had 3,146,854 entries. Now there are 5,022,103. There’s no indication of the years or places added.
As with most large indexes on Ancestry from printed material, the index was created using text recognition software.
As a word of warning, such registers are often promoted as a way to fill in between decennial censuses. But be aware that the registers appear to have been compiled in advance. I find a great grandfather registered to vote in a place he’s known to have left the previous year.
Findmypast’s collection England & Wales, Electoral Registers 1910-1932 includes over 20 million entries for Lancashire with better supplemental material than Ancestry.
MyHeritage does not include UK electoral records.