The average temperature of the battery, followed by its average state of charge through its lifespan, will have much more effect on battery life than the sticker on the casing.
Since it takes a long time to charge from 80% to 100%, but can be drained from 100% to 80% quickly, the voltage allowed by the vehicle's voltage regulator will play a huge part in how quickly and closely it is returned to the ideal 100% state of charge, which in a vehicle, is basically never.
So it is likely the battery is junk. Most starting batteries are. Most are designed to last only the warranty period and a day, and battery manufacturers are doing their best to cheapen them to this ideal max profit point and spending part of that profit on marketing.
A wise person wanting to make the battery last far longer than the warranty period, would protect it from engine heat as best as possible, and use a grid powered charger to top it off every so often, and asap after any significant discharge of it.
Average state of charge, and average battery temperature. Both of these can be influenced by the vehicle owner to some degree.