Highly unlikely it’s leftover stock. The BB date wouldn’t stretch this far for most of the items there. Eg the a lot of the Celebrations festive pouches from last year were BB 02/23. Quality Street were 06/23. Some of the Puds batches were 03/23. Even if some batches were manufactured later it’s still unlikely they’d be in date now.
Impulse lines sell out first typically and they’d be the first to be RTC after Christmas is over (if any stock was left over). Anything which any sort of Christmas graphic will have been RTC. It isn’t the same situation like with leftover Lindor boxes which will be on retailers planograms in their confectionery aisle anyway, so would just be simply moved over there.
Plus all this stuff is date checked on a rota basis. Please don’t spread misinformation.