Which performing arts loyalty program innovation first introduced the concept of 'flexible subscription' that allowed patrons to choose performances throughout a season rather than committing to specific dates?

The performing arts industry has evolved significantly in how it builds audience loyalty and retention. Theater companies, ballet troupes, and symphony orchestras have all experimented with different loyalty program structures to maintain steady attendance and build dedicated patron bases. This question explores a pivotal loyalty program innovation that transformed how performing arts venues approach audience development and retention.

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The Metropolitan Opera's 'Met Membership' program (1987)
Steppenwolf Theatre's 'Audience Rewards' system (1999)
Theatre Development Fund's 'TKTS Plus' (2001)
American Repertory Theater's 'ART Card' program (1995)