User blog comment:Wythagoras/Graphs/@comment-25418284-20140912051338/@comment-5529393-20140912054731

Certainly. If there is a longest sequence of graphs {G_i} such that G_i has at most n+i vertices and no graph is a minor of a subsequent graph, then adding restrictions like planar and minor will only reduce the number of possible sequences, so there will still be a longest sequence, and PSSCG(n) is defined for all n.