Some regulatory agencies require that a backup set is available to be used if the primary chips are compromised. Some require a full set of backup chips; other jurisdictions only require that certain denominations (typically $25 and higher) have backups available. The base color of the backup chip is sometimes required to be the same as the primary, but that also varies by state regulation. Most of the time, only the compromised chip denomination is exchanged on the casino floor.
But there have been some instances where both the primary and secondary sets have been used, but typically not simultaneously. The Empress Casino (Joliet, IL) had both sets in play, as did the Par-A-Dice Casino in East Peoria, IL. I don't know the particulars of why either secondary set was utilized. I'm sure there have been others, too.