The bonds were broken up and packaged into three or four classes I think, and then were renamed Baby bonds. The principal would be the amount the bond was issued at back in 1999.
Is the letter just addressing physical certificate holders, possibly? With $4 million face of bonds that were held in physical form? Certificates to be redeemed? Electronic holders paid off by ETF? Just thinking out loud. BTW I tried to find an April 1 date on the letter but there isn't one.