How have courts used the felony murder special circumstance findings to demonstrate that instructional errors on other aspects of the murder instructions are harmless?

The rationale for relying on a jury's felony murder special circumstance findings to show that instructional errors on other aspects of the murder instructions are harmless is that "the elements of felony murder and the [felony murder] special circumstance coincide," so the jurors necessarily found all the elements of first degree felony murder. (People v. Elliot (2005) 37 Cal.4th 453, 476.) It is not invariably the case that they coincide, however, so we must be careful.