Sorry, I wasn't clear. I didn't meant you could get 120GB of storage for a year, I meant you could each year buy 120 units of "GB-month" (like kWh but for storage).

You could distribute that equally throughout the year, using 10GB-month per month, yes. Or you could use 1GB-month in the first month, 2GB-month in the second, etc, as your storage needs grew.