1866
($3,000/12,500),
1867
($2,500/12,500) and
1873
open 3 ($2,500/12,500) are equally the next most difficult dates to find in full red.
1866 PCGS MS66RD
1871 PCGS MS66RD
1871
($4,000/15,000) actually has a slightly lower mintage than 1872 and ranks third in value.