To clarify, the design that the paper is addressing is the ARC, a full-size pilot reactor intended to put 200MW out on the grid for 9 working years. The demons

To clarify, the design that the paper is addressing is the ARC, a full-size pilot reactor intended to put 200MW out on the grid for 9 working years. The demonstration reactor is the SPARC which is based on a scaled down half-sized (but 1/8 the mass and 1/8 the cost) version of ARC. While the main goal of SPARC is to achieve significant net power output, along with a proof-of-concept for many of the design features of ARC, some features may have to be left out for lack of space. So I don't know if SPARC will be able to achieve net tritium breeding, but I presume they will be testing as many of the features as they can along with taking measurements and verifying the model. It is also noteworthy that the ARC/SPARC design allows for replacement of the vacuum vessel and cooling blanket without complete removal of the outside magnetic coils, so they foresee design iteration of those components unlike the ITER design which will be pretty much locked in.