Although similar tactics had been developed some 20 years earlier there's no guarantee that those in authority remembered it and made the connection!
Bomber Command's Operational Research Section did conduct some analysis of damage to returning aircraft. The AHB monograph on OR in the RAF states that research was carried out into damage caused by AA fire; "the great majority of aircraft damaged by heavy flak received only two or three strikes [but] strikes from below were twice as numerous as those from above." That in itself is hardly surprising, given that AA fire usually has an upward trajectory...
However, Schraege Musik may have been so effective that very few crews returned to report attacks. It's unlikely that intelligence on its use would have come from POWs or SIGINT, but it's hard to believe that we had no hint of it.