But that does not imply that monetary policy can guarantee an absence of booms and busts, or eliminate the business cycle. To begin with, the "trend of potential output" is not something which can be seen, felt, or measured. For this reason, it is impossible for any central bank to be sure when actual output is above, below, or equal to it.
Rough calculations can be made of course, adding assumed growth in the labour force to assumed growth in productivity to come up with a ball-park number. But growth in the labour force can vary for all kinds of reasons, including in particular because of abrupt changes in net migration.