Tilt Brush Toolkit (unity) Creation Version

Looking at the tilt brush toolkit and planning to explore it a bit.
The first thing I did was try Tilt>Toolkit>Export Brushes for Toolkit
It appears to have started exporting a bunch of my custom brushes and got this message
" TBT brushes must have a valid creation version"
any idea how I choose a number for that and how the logic works.
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