We host and participate in many different IPT tests. These tests are performed using the same methods, homogenous material, and same instructions...comparing different methods on a 1:1 basis does not reflect the true goals of IPT testing.
On a sidenote however, we will perform testing on same materials employing different methods, however, this is not on a 1:1 basis, the comparison is more along the lines of 10 labs employing method A, 10 labs employing method B. Both methods are separated for statistical analysis, but often are plotted on the same chart...when this is done it's interesting because you can quite often see which method is more precise and to some degree how precise it is (not that it's news) just interesting to see empirical data which gives you a solid visual representation of the methods' accuracy.
Anyway, I would suggest you contact whoever is hosting this IPT and clarify further with them, employing different methods typically will not give you a valuable end result.