Also. Recording a 10kHz signal at 0dB does not generally produce a 0dB output on playback due to the high frequency compression that is normal in the analog tape world. I have always recorded the 10kHz tone at a level of -10dB. At that level, the tone should play back at -10dB because the level is below the high frequency saturation point of the tape.
Hmmm, well both of my decks are giving me a near 0 dB reading during playback of a 10 K tone recorded at 0 dB. Perhaps the machine(s) you worked with were not in pristine condition?