The miles accelerator bonus only last for a period of time, so its very possible that it has now gone. I think it just depends on loads etc - once a certain number of tickets are sold it disappears.

Slightly off topic, but I find the appearances of miles accelerator have diminished considerably over the past couple of years. Whereas I would be getting them at least once a month, I don't think I have had one instance in the past 9 months, and even before that it was reducing. Maybe its just down to my routes, and others experiences are different... I suspect not though