I suspect the huge costume cupboard is now being used to store the huge amounts of paperwork that are constantly being generated to satisfy the demands of the latest government initiative.
The junior school I work at does still have a big costume cupboard filled with stuff from years back, mainly because I don't think anyone would dare take it away from the teacher it belongs to, who's been there 20 years.
'Mrs T's cupboard' has a rail down one side - about 10 feet long, with dresses & other clothes hanging on it, the rest of the cupboard is stuffed full of boxes - we have boxes of kilts (from MacBeth) boxes of victorian mobcaps, hats, belts, tights, masks, all kinds of props. It's a fascinating place. Every year, once the plays are decided on we dive in & pull everything out & decide what will do for which part, what can be 'made-over' & what will have to made from new then we find parent volunteers to do the sticking & sewing. Dresses & costumes are tried on & the parent of the child that's going to wear it will be asked to do any minor repairs & alterations.
I remember one year the same tricorne hat was worn by a prince in 'Cinderella' (Year 3) a town crier in 'The Golden Goose' (Year 4)and a Lord Mayor in the Victorian play the Year 5s wrote themselves
Parents of mice, birds & other supporting animals are usually asked to provide tights & a T shirt of the appropriate colour & TA's then make a paper hat-type 'mask' - we don't usually keep them as they are too easily crushed.
Sadly I imagine the cupboard will not long survive the retirement of the teacher in question in a couple of years' time & we'll have to resort to asking parents each year.