Henry,
XRF Analyzers are very limited AND highly inacurate. You can measure the same material twice, and get 2 different results.....do it a third time and you maybe get a third result.
I really don't think that it can be determined if the material is for low or high temperature applications, without a destructive test, ie cut out a sample of each pipe.
I recently dealt with a P91 flange which had low hardness, one of the leading metallurgical companys in europe was brought in, they suspected low carbon content was the reason why full martensitic structure was not present, they asked for permission to cut out a small piece of the flange in order to take it to the lab for further investigations. The contractor, which at that point still thought they had a chance to save the flange, refused the destructive test.
Later the flange was rejected due to "uncertain non martensitic structure"
They explained again and again that in order to do a PROPER investigation of the carbon content, a sample had to be cut out......they both had a Phd. in metallurgi.
In regards to OP's problem, it is not only a matter of CS grade, without correctly transfered heat numbers you can't be sure of the materials origin, has the correct test been done, etc, etc...Which in some parts in the world is rejectable in the first place.
3.2