If your printer prints a pound sign below, it means hash. The number N must be a number and not a variable, and lie between 1 and 255. This means that the second item of data read from the tape is the second item of data which has been recorded on the tape. It is not possible to 'skip' to say the 6th item of data without reading everything in between. You should only have one file open to CS1 at a time, otherwise the computer will lose track of the data on the tape.
Any unused tape is filled with nuls.
A number always occupies 9 bytes, and a string one byte more than the string has characters. When the computer is saving data, it does so one field at a time, amd it is essential the computer has control of the cassette motor. If you have purchased a third party lead and require the polarity reversing, you should ask your supplier to do so. It is possible to swop the wires yourself, but with some systems there may be problems as the screening may be broken. If you used long field lengths when saving the data, you MUST specify the same length in the OPEN statement to load the data.