How long was the preamble? Do you think the preamble needs to be a fixed length, or 'just enough' to sync?
The "preamble" is over a minute long, which is ridiculous! And, there is an interrecord (or interfile) gap which is several minutes of 1/0s long. You should need only a dozen or so 1/0 cycles to synchronize the recovery clock PLL, if that method is preferred for decoding.
I can't imagine why they wasted so much time and tape for that.