we get the framework of your question - its in relation to BFO action on 'ancient' typically general conversion receivers, that lacked a proper product detector.
an AM signal off course is 2X or more wider than SSB, especially if we want more spectrum into our headphones. the 2nd xtal filter is too narrow for AM signals - for both sidebands to pass through. but some may have added a product detector after the first 45 MHz xtal filter. try a search engine to see who has reported results adding an envelope detector -- uBITX envelope detector or AM detection. BTW, an envelope detector is pretty much a simple diode - but it has to have appropriate gain in front of it (but it might not take much for huge 41m AM signals. others add a SDR at 45 MHz that would also be a good AM receiver.
I appreciate your inquisitiveness. Too easy for us to miss context of your question, not presuming product detector behavior.