That totally misses the point though, because if the website only validates on the basis of extension and accepts the format in an unrecognised format, the backend won’t know how to handle it anyway. There’s no point uploading a HEIC file disguised as a PNG (or whatever) if eventually somewhere along the workflow an examiner is actually going to have to open that file in a program that doesn’t know how to parse HEICs.

Perhaps the examiner’s program accepts HEICs and the frontend was unnecessarily limiting. Many systems are like that, and it’s frustrating that the College Board’s wasn’t.

The examiner’s client program is likely a browser that connects to a web-hosted system, and with the exception of Safari, other browsers do not (yet) handle HEIC natively nor even gracefully.