>>106020857
One thing most cassette purchased at Kmart and similar places had that were removed from data cassettes was the leader. More than once I saved something at the start of a cheap tape and didn't remember the tape had a leader on it that needed to be moved past before anything could be saved. But after the pain of doing it a couple of times, I learned to always check.
Pic related seemed to be in every computer magazine of the time. I don't see it mentioned in the ad but they were leaderless tapes. Ten minutes was more than enough for all but the longest programs full of data. Think the only time we ever went over was when we had a mail merge program for the church directory. That required flipping the cassette over.