I done the same thing, sending 2 samples to separate labs, on 2 occasions.
AGAT vs FluidLife, & AGAT vs Blackstone.
I also found that Blackstone test came back with different results than AGAT.
Fluidlife, & AGAT were quite similar, & I have stuck with AGAT just because I can drop off my own samples, & do not need to spend any thig on postage, or shipping.
I was mostly concerned about fuel dilution. Both AGAT, & Fluid Life us Gas Chromotography, where Blackstone used an interpolation method.
AGAT flagged my samples, with 3% fuel dilution, & Boron depletion & recommended oil change, while Blackstone suggested my samples were thin but no fuel dilution.
Thanks for your info. AGAT was another option I was considering. I may do this again with CAT and AGAT for fun.