A friend of mine recently downgraded to 2.1 without any backup, and after dumping the OTP file, he upgraded using cartidge, thus got a old 3DS with a system version of 9.5.0-4J.
So the question is, is there any method of entering HBL (then downgrade to 9.1)? We've tried ninjhax2 and browserhax, but none of them worked.

 

https://github.com/Plailect/Guide/wiki/9.2.0-Update

The numbers in the body of the chart refer to the last number of your version (which corresponds to the browser version installed to the system). In the case of "5.0.0-7U" for instance, you would follow the ">6" guide in the 5.X.X column because -7 is above 6. If you had "5.0.0-4U" however, you would follow the "2-6" guide in the 5.X.X column because -4 is between 2 and 6.