I have a High Fidelity magazine ad from July 1954 showing RCA's first stereo release ECS-1 Strauss/Reiner priced at $14.95. Sixteen monaural tapes were also offered, including the budget Bluebird Series, priced at $12.95.
The ad doesn't mention the format, but I suspect ECS-1 was available only in the staggered/offset/displaced format, as the stacked/inline format had not yet been commercialized in 1954. By 1956, however, nine classical tapes were offered (through ECS-9) in both staggered and stacked formats. The 'displaced' version had a "D" following the three letter code, e.g. ECSD-9. These early duplication tapes were on unmarked reels, had labeled leader tapes attached, and were in generic (non-picture) boxes.