Can i subscribe to a month that has passed by already

Hello there, useramorgan92705.

I'd like to verify what you meant by subscribing to prior months so I can walk you through from there. When subscribing to QuickBooks the start date of the subscription will the current date. Billing happens overnight, so the charge does not occur until after midnight. 

However, if you're referring to bank transactions you want to enter into QuickBooks Self-Employed from previous months, yes it's possible. You can either connect your bank which downloads up to 90 days of transactions or manually enter or import them. 

Any additional information about your concern is much appreciated. You can always post them. Take care and have a great day!