Perhaps label owner Joe Evans simply just kept recycling existing tracks on subsequent releases to save money on recording new tracks to use as flip sides.
This extract from the Carnival list of releases (from Dave Rimmer's site) indicates that I Wanna Be, Hearts Were Made To Love, Just You Wait & See, What Is Love and Sweet Potato Gravy were all used more than once ...
Carnival 548 - I Wanna Be (Your Everything)* / Sweet Potato Gravy (Instrumental)
Carnival 550 - I Call It Love / Feelin' Good*- 1970 *Flip By The Carnival Kings.
Carnival 552 - I Wanna Be / Hearts Were Made To Love - 1970
Carnival 554 - What Is Love / Sweet Potato Gravy (Instrumental)* - 1971 *Flip By Maurice Simon & The Pie Men.
Carnival 556 - Hearts Were Made To Love / For The Rest Of My Days — 1972
Carnival 557 - I'm The One Love Forgot / What Is Love - 1973
Carnival 558 - Just You Wait And See / I'm The One That Love Forgot — 1974
Carnival 559 - Just Be Yourself / Just You Wait And See — 1974