RCA had a big vault cleanout in 1959 or so where some Sun tapes and the binaural tapes were dumped. The Binaural tapes were sometimes just considered "safety" tapes and had no practical purpose once they were used to mix down to make the mono master tapes. The "safety" tape came in when they simultaneously made a binaural and a mono tape. RCA never got ALL he tapes from Sun, a few of the Sun sides had to be mastered from 78s or 45s such as Milkcow Blues Boogie, You're A Heartbreaker, and lost the tape for Baby Let's Play House. RCA did make a master reel of the Sun material with added compression and reverb that was the basis for just about ALL he RCA Sun releases whether separately or in compilations until Elvis At Sun came along. LP and EP or Single masters often times varied with the Sun material and other material. Typically the LP version had even more compression and reverb that was added while the tapes were mastered to lacquers.