To my knowledge, they never used the number boards for anything but the engine number, no "X" no "1-" or "2-" for first or second sections.
I've always wondered why the 470 and 480's even had them to begin with. Perhaps it was one of those "standard practice" things where previous SG engine orders had them, so Alco and BLW put them on these too because someone neglected to tell them not too. On the othe other hand, they weren't used to display SG train numbers either.
Just one of them things to drive us nuts, I guess.
BTW, when the D&S put them back on the engines in 1981, they briefly used them to carry the train number. I don't think that lasted very long, but somewhere I have shots of 481 in Silverton with "463" on its number boards.