I tend to agree. The TOCs in Wales are FGW, who are disallowed, Virgin West Coast, ATW and Cross Country. Most of South Wales is disallowed by the presence of FGW, with the exception of Caldicot - Lydney, which all have only 2 platforms. Mid Wales is ATW only. North Wales fits the two TOCs with Virgin and ATW, but I can only think of Lud Jn and Holyhead with 4 platforms.
Llandudno has 5 platforms, but 2 are out of use. It is still mechanically signalled so surely the box opened before 1985. It is the best I can come up with, but I'm not submitting it.