Barding for small / medium animal companion: same, or different item?

[ThatGuyDM]

Recently got a Mature, and thus bigger, companion, that went from small to medium. RAW, does the barding he wore no longer work, or is it strictly "small/medium" barding, and works either way?

[breithauptclan]

Well, here is the table for barding.

It lists the small and medium barding on the same line.

And that is really all that RAW says as far as I can tell.