I wonder if the tape is a late issue. Near the end B-C gave its fans the warning that they were going dark and there was one last chance to order. Tapes from those last days don't have the same level of quality control that was the hallmark of their earliest efforts. In any case even for a very good B-C tape there was occasionally an audible difference, usually very slight, from side A to side B. Also, although their literature said they used an Audiotape formulation, thankfully they changed from that early on and were using a very inexpensive Ampex duplicating formulation from the 600 series. My experiments (on Scully 280's and RS-1500's) at the time lead me to the conclusion that while the tape had decent low level performance it had only modest headroom in the mids it had very poor headroom at both frequency extremes. Had to keep the max. levels way down when using that tape on voice, piano, anything exposed. Now that didn't stop B-C from making fine tapes, it just meant that they had to walk a very fine line between max. level and ultimate signal to noise when making their running master and setting levels on the dupes, and perhaps in this instance they went a bit off the line.