"The drive rewound the tape until it got the start...and kept going."
On all the mainframe decks I worked with - the relatively short leader tape was not fixed permanently to the deck's take up spool. If on a rewind it missed the data tape's physical start marker*** - then the leader tape ended up flapping round the data reel. The tape feed equalisation sensors (weight or optical) then shut it all down. Some gentle handling was possibly then necessary to recover any thrown loops.
*** usually a short transparent section of tape. In the early days the operators had to make these themselves - especially if a tape had had to be repaired by lopping a bit off. The section's ferrite coating was removed with acetone - which came in large brown bottles. Unfortunately the head cleaning iso-propyl alcohol came in identical looking bottles - and both were a clear liquid. As tape deck heads were cleaned quite often - it was not unknown for their insulator separators to be dissolved by acetone in error.
Biting the hand that feeds IT
