Collected information at short notice? The reverse! (4)
I believe the answer is:
data
'collected information' is the definition.
(I've seen this before)
'at short notice? the reverse' is the wordplay.
'short notice?' becomes 'ad' (short for advert; 'short' indicates a short form).
'the reverse' is a reversal indicator.
'at'+'ad'='atad'
'atad' written backwards gives 'DATA'.
(Other definitions for data that I've seen before include "tables, perhaps" , "information from bank" , "Collection of bits of information" , "Gathered stats" , "Series of measurements" .)