Brendan Owens and Saso Strle completed the computations for knots of 8 our fewer crossings. References are listed below.
K. Morimoto: On the additivity of the clasp singularities, Kobe J. Math. 3 (1987), 179-185.
H. Murakami and A. Yasuhara: Four-genus and four-dimensional clasp number of a knot, Proc. Amer. Math. Soc. 128 (2000), 3693-3699.
B. Owens and S. Strle: Immersed disks, slicing numbers and concordance unknotting numbers (unpublished).