I was wondering about the 88% number, so did some digging and reaching out.
First of all, that figure is out of date - a good number of months.
Second, it appears to include ScotRail, Merseyrail and Transport for Wales ticket sales within it, as well as including sales records that are essentially back office accountancy/not actually a real paper ticket sale, albeit it is technically a booking office transaction, just of no consequence to a passenger.
The net effect of this is that smart ticketing in Scotland is only just starting to emerge, and adversely skews the 88%. If you strip ScotRail out, and Merseyrail, and look at more recent sales data, so essentially just for England and Wales excluding Merseyside, ok it fluctuates by period, but it's already in the low-mid 90s consistently at least recently.
RDG may have missed an opportunity to provide even more convincing statistics, although I suspect this data was prepared some time ago based on the last complete financial (rail) year.
By the end of just the next railway financial year, I'd be confident in betting the house on 95% or above utilising smart ticketing IN THE AFFECTED AREAS OF ENGLAND.
Incidentally one of the stubborn areas is One Day Travelcards, which should disappear soon anyway, making the number pretty impressive.