Mo Pinel on Interchangeable thumb and ball dynamics:
Storm, MoRich, and the USBC did a study comparing balls drilled with the interchangeable thumbs, with different sized slugs, and balls drilled without slugs. The difference in ball dynamics (mass properties) were within one standard deviation. Therefore, interchangeable thumbs, or slugs, make NO difference to ball dynamics.
The study I referred to was an empirical study, not a theoretical study. The results were verified three times. In my opinion, the results are very accurate. No change in the drilled mass properties when using slugs or interchangeable thumbs. Good enough for me and the USBC Equipment and Specs. Dept., who did the actual work on the study.