Yes calamansi Juice does eventually expire and it loses it's freshness after the expiration date passes.
For the best taste and health benefits of calamansi you should consume the calamansi expire juice before expiration or at least on the expiration date.
You should always either freeze the calamansi juice or keep it refrigerated when not drinking it.
As long as it remains frozen the calamansi can last for 1 to 3 years but in the refrigerator it goes bad much sooner.
Same thing with regular lemon juice it should always be refrigerated or frozen otherwise it goes bad and spoils pretty quickly.