You're quite right about the AK being reengineered at times. Indeed, there were several variations of the AK-47 alone and the earliest attempt was a sheetmetal fabrication ('48-'51) which was abandoned for milled steel ('51-'54). Even the machined receiver model was modified again ('55-'59) and it was probably this third model which was brought to the attention of U.S. Intelligence. The Russians certainly didn't rest upon their laurels and do not hesitate in using new technology as they perfect it.
Thank you Sir Edmund.
(P.S. for those of you who haven't been here for over a year, Edmund Rowe was dubbed "Sir Edmund" at The Firing Line for his wonderful discourse on the AR15. It's well worth digging up.)