How many SIMs does Data Usage remember? The Data Usage screen of Android seems to remember data usage per SIM. What I want to know is how many SIMs does it remember before deleting the old ones or does it not do that?

With my carrier it's cost effective to activate a new SIM (heavily discounted) every month so was wondering how much data the Data Usage screen would take up.
Each time you change the sim card and use internet, The data will be added up to the previous data. In lollipop, The Data usage moniter screen will show the entire data. If u want to clear that, You have to Root the phone or Reset your phone.
There are many third party apps on Play store to Record usage. And u can also customize them for your need.