You read the paper about calibrating the signals, that's a reasonable takeaway. There's a different paper about how the 4 independent algorithms were tested to

You read the paper about calibrating the signals, that's a reasonable takeaway. There's a different paper about how the 4 independent algorithms were tested to make sure they did the right thing with simulated data: ring, crescent, disk, double point source. That's the process that you had an incorrect takeaway from the documentary about. The filmmaker is a member of the collaboration and was highly involved in the imaging. First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85/pdf https://iopscience.iop.org/article/10.3847/2041-8213/ab0e85/... You'll have to follow the footnotes to find out the ages of these algorithms; CLEAN was invented well before I first used it in 1985, and I first ran into maximum likelihood in 1987 or so.