Possible Clues:

• Period between reigns
• Time during which there is no active monarch
• Period during which a throne is vacant
• Period between periods of normal rule
• Period between successive reigns
• Break in continuity aroused regret in miners' union
• Gap in continuity true men grin about
• Merge in turn is ordered when there's a gap at the top
• False men ring true when throne is unoccupied
• Gap at the top all but buried by tail-end of working miners