Individual extension numbers were added at a steady 36,000 a month between July-September, and had even dipped to under 20,000 between September-October. However last month showed a huge rise of more than 60,000 - trebling the previous month's rise.
Commentators are unsure if it is an anomaly, or likely to be the usual number of monthly sign-ups, as the service becomes more well known.
"To my knowledge the only recent change is that the DMA has advertised the CTPS in the trade press, and that the dip was due to it being the summer," says Experian director of B2B marketing Richard Lloyd.
Lloyd said he supports best practice and the notion not to call people that don't want to be called. However, Experian is currently analysing take-up rates by company type to satisfy itself that limited companies, for example, aren't just adding tens of numbers indiscriminately.
According to Corporate TPS, 15,272 companies are responsible for the total number of extension lines added - a crude average of 12 numbers registered per company.