Air Arms Owners Club

Good Day
Is there anyone who can advise me of the history of the S400 SL Xtra FAC .177 with side level cocking lever.
I have purchase this rifle recently and have been advise there was a limited number made by Air Arms.
What year were the S400 SL Xtra FAC .177 manufactured ?

Have a read here: https://www.airarmsanorak.co.uk/air-arms-s400-s410 & https://www.airarmsanorak.co.uk/the-s510

Thank you for your reply Rotherham Owl, greatly appreciated