I have flown a Piper Seneca Five at FL230 on oxygen. On the Five I was still seeing 800 fpm passing 20000 feet yet the service ceiling is quoted as 25000 feet. I have heard of a Piper Seneca Five topping nearly 30,000 feet in the right conditions.
Beyond quoted service ceilings is possible be interesting to know what others have been up to in their aircraft? and the highest you have been unpressurised on oxygen.
in this situation there is no reference to the flight being a record attempt or the reasons for the pilot being incapacitated which could have been something other than lack of oxygen.
Also to consider are air conditions which could have lifted the aircraft to those levels which is a very real possibility.
Pace