I don't have a "good" answer but I do have some answers.

Per +++ MIDI.ORG +++ the main distinction between MID and SMF files appear to be where the file originates.
Quote:
(SMF) files are typically created by a "MIDI sequencer" (software or hardware) and then played on some kind of MIDI synthesizer.
. I gather from this that SMF is somewhat hardware or software specific whereas a MID file is more device agnostic and computer orientated.

+++ THIS +++ site by the US Library of Congress indicates a SMF file can contain additional data not specified in the MID file specification.

Jim Fogle - 2025 BiaB (Build 1128) RB (Build 5) - Ultra+ PAK
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