The massive (up to) 50% off posters in the shop windows belie the fact that most items in store have only been reduced by 10% or 20%.
A small number of items are 30% off and in the 2 stores I visited (whilst passing by - I didn't make a special trip) I didn't see much of interest 50% off.
So, my guess is that the administrators will be transferring all the tangible assets to a new "trading" company (leaving the debts of the old company in a separate legal "entity") and hence whatever they get for the stock will help to pay their fees....and they will know roughly the monthly turnover and what timeframe they expect to sell all the stock off in.
Hence they don't need to have a big sale yet...but I assume that the larger stores (with higher rents and staff costs) will be closed sooner and stock will be moved to cheaper stores in order to keep them "topped up".
The unsecured creditors are not likely to get much and the secured creditors will get something back from whatever turnover is achieved during administration (after fees).