Lot 61628 – 1921 15c blue on buff imperforate proof sheet

1921 15c blue on buff, the impressive imperforate proof sheet of four, printed in the issue colour on an experimental paper, huge margins and large spacing between stamps, filing hole at top right in margin and vertical crease, both of no importance for this, the only recorded complete proof sheet, of great importance as only two additional singles are known; cert. Bortfeldt (2008).