Are we talking cloth or leather?
Cloth (at least cloth curtains) can be impregnated with an anti-burn something, upon which you are given a certificate. This was good enough for a commercial buildings insurance and license-to-use. Companies can also spray that stuff onto things that are hard to remove and put in a washing machine (aircraft seats for instance). In case of the building I was managing at that time, the stuff they put on (and thus the certificate) was good for five years, after which a reapply was needed and a new certificate issued.
One night we accidently left a skylight window open and somebody tried to set the curtains on fire. Needless to say, it didn't work - we only had some scorch marks which the insurance covered. Even one of our volunteers, a fire chief, was impressed.
So, instead of going to great lengths in getting a new burn certificate, or getting your existing upholstery tested (but where would they take the sample from) you might just consider getting them burn-treated once more.
Oh, and the requirement for burn certificates, impregnation of cloth and things is typically not that it cannot burn at all anymore, but only that the burning stops within a certain time or distance as soon as the ignition source is taken away. Or even just that the flame front doesn't propagate at more than a certain speed, giving you ample time to evacuate. So don't think about testing in-situ by putting a propane burner against your interior. (On the bright side - that will require a new interior and you now know what to ask for from the upholsterer, do you?)