XNL63a 1991 NI 39p bright mauve Fluorescent Coated Paper (FCP)cyl Q1Q1 block

1991 NI 39p bright mauve issued on non-phosphor Fluorescent Coated Paper (FCP) instead of Phosphorised ACP (no afterglow under UV – effectively a missing phosphor error) in cyl block of six Q1Q1. Only a handful of such blocks are believed to exist. Spec X