Speaking as someone who actually used toe clips, I'd like to chime in.

What most people refer to as toe clips are actually a toe cage and strap. You can put them on either platform or cage pedals. The clip is the third piece of the puzzle, and bolts to the bottom of the shoe. It's sort of a wide, flat clothes pin which engages the cage part of the pedal. Once engaged, the strap is pulled tight, preventing the clip from disengaging. You can use cage and strap without the clip; in fact I haven't seen a clip in at least 15 years. For some reason, common usage still refers to the setup as "toe clips," regardless of whether or not a clip is used.

A platform pedal was not reversible. At the front it had holes for mounting a cage, and at the rear it had what could be described as part of a cage. The purpose, of course, was lower weight compared to a full cage pedal. They had just enough hardware to secure a cage and strap. Then clipless came along and made them obsolete.

Clipless, of course, is so named because the 'clip' isn't used anymore. But you still "clip in" to engage. Go figure!