For a while, U.S. has targeted X% inflation. What happens if we sell a 100 year bond at Y% yield and then in 50 years economists learn we should target less tha

For a while, U.S. has targeted X% inflation. What happens if we sell a 100 year bond at Y% yield and then in 50 years economists learn we should target less than Y% inflation? In that case are we stuck between either the bonds growing faster and faster and faster than the dollar, or being constrained in inflation targets?