We'll have to talk to PBO about that. My guess is that it is based on estimates of take-up, and I think it's fair to say that all of us are making guesses about what the take-up will be. So different guesses are legitimate. Ultimately, as with other benefits like this and tax credits, it's difficult to estimate what the take-up is going to be. However, we're happy to follow up with PBO and work to understand the discrepancy.
On May 7th, 2019. See this statement in context.