To get a good hole-fill on through hole solderjoints with protruding leads, it is necessary that both the surface solderability and the thermal solderability together with the specific soldering distance be within the specifications for the process to be used. For wave soldering with tin-lead solder all these solderability demands are specified in the book Soldering in Electronics from R.J. Klein Wassink. Only when these demands are met, one has a good basis for a reliable soldering process.
Often the board design has a main effect on the thermal solderability of certain joints. If not the correct design rules regarding this thermal aspect are used, solder-fill to the top of the board surface will often be impossible with the allowed solder process settings. A second soldering operation will in general not improve this result as will be explained.