I got 25000ft on mine. But really, it depends on your exact type of engine.
Anyhow, I'm sure it's capable of restarting above FL250 with the master and ignition on and the IAS above 300kts. No reason not to.
That's like saying it can ingest 20 lb birds as well.
The facts are that it could only reliably demonstrate restart in the published envelop
of course your mileage may vary but don't depend on it