Hey TJ! The way that our number recycling works is actually based on an internal algorithm that changes based on different factors per account. So I'm afraid that I don't have a simple answer for you.
As a TextNow user, however, you should be receiving warning text messages about your number being recycled if not used within a certain amount of days. That same warning message is also sent out to the email address on file (it may be going to your spam/junk inbox)
Since we have a finite amount of numbers available, we do have to exercise efficiency with our numbers (meaning that numbers that are inactive are recycled to give another user who is active a chance to be assigned a number)
Luckily, your previous number was still available, so we've reassigned it to you. Please note that this is a one time exception, and should you lose your number again in the future, we won't be able to recover it for you.