Mexico, Scott 1541c, MNH.  1990 overprint of the 1988 Cesar Vallejo issue, unexploded booklet containing a pane of 5 with red label in middle overprinted with MEXICO CHICAGOPEX '90 souvenir cancel, very scarce as this booklet was on sale for 1 day only at CHICAGOPEX. Fresh, bright & VF+. 2023 Scott CV: $250.00.