Reading the linked article below, it appears the bomber was a ball of flames before impacting the ground. At the time only one body of the three were found. Sgt Crowther was recovered at the time but nothing was ever found of his two American colleagues, apart from an identity bracelet belonging to Montgomery. The other two crew members we were considered missing in action “MIA”.

Just a absolute guess, the intense fire and impact destroyed most of any remains.

It wasn’t until a local aviation archaeology group attempted to excavate the crash site in 1974 after historian Andy Saunders located the most likely area of the crash.

However, it wasn’t until 2019 the site was throughly checked for the remains of Lt Montgomery and Sgt John Holoka.

After multiple excavations, finally the remains of Lt. Montgomery were found. It took years to confirm his identity. https://www.aerotime.aero/articles/mystery-of-lost-ww2-pilot-solved-after-remains-identified-79-years-after-crash/amp