Aside from the color difference at the edges, the chips are identical. It could very well be that one was from the "back-up" rack as back when these chips were current it was highly unlikely that BOTH were on the tables at the same time as it just wasn't done! Just because it may have been a backup chip, doesn't mean it wasn't used on the tables. The original "in play" chip (whichever it was) could have been pulled from play and replaced with the backup rack chip for reasons unknown. This is a fairly routine practice even today.

Steve