Can I get history from before I was using TezLab?

Unfortunately, this isn't possible.

In order to capture data from Tesla vehicles, it must be captured live while the vehicle is online. There is no ability to download the activity of the vehicle after the fact.

While Tesla may store information about vehicle history on their end, it's not available to be downloaded. In fact, nothing you see in TezLab is downloaded "as is" from the car. Tesla vehicles only share their current state. Everything you see in TezLab is calculated by taking a series of snapshots of the vehicle's current state at an interval. These snapshots are then processed by us where our systems track changes and stitch it all together into what you ultimately see in TezLab as drives, charges, etc.