They certainly don't have any on Sunday afternoons, for sure - they removed these some while ago as demand is great enough such that they don't need to offer any as they can sell enough 'ordinary' tickets to fill their trains.
Engineering work can affect the offer too - Crosscountry have these affected
Sunday until 1040 and from 2300
The 0915 Bristol Temple Meads to Edinburgh and 1030
Bristol Temple Meads to Glasgow Central will depart
Bristol Temple Meads a few minutes earlier than
cheduled.