Here's an update of the Redbreast Cask Strength releases to date.
B1/11. 57.7%
B1/12. 58.6%
B1/13. 59.9%
B1/14. 58.2%
B1/15. 57.4%
B1/16. 57.2%
B1/17. 58.2%
I'm not aware of any B2/-- so far. I've heard rumours but never seen one.
The B1/14 is the hardest to find as it's not in the EU market. It was only available in the US and South Africa to my knowledge.
If there's additional information on these or other I'd be happy to hear.