All liability for contributions to the Combined Fund that arises on and after , shall be determined exclusively under this chapter, including all liability for contributions to the 1950 UMWA Benefit Plan and the 1974 UMWA Benefit Plan for coal production on and after . However, nothing in this chapter is intended to have any effect on any claims or obligations arising in connection with the 1950 UMWA Benefit Plan and the 1974 UMWA Benefit Plan as of , including claims or obligations based on the “evergreen” clause found in the language of the 1950 UMWA Benefit Plan and the 1974 UMWA Benefit Plan. This chapter shall not be construed to affect any rights of subrogation of any 1988 agreement operator with respect to contributions due to the 1950 UMWA Benefit Plan or the 1974 UMWA Benefit Plan as of .February 1, 19931993-02-01February 1, 19931993-02-01February 1, 19931993-02-01February 1, 19931993-02-01