The fact that BCO's dont ask gives a bit of a clue ... they don't have to, because they know that the lintel will take the loads as the mannufacturers have designed it to
LIkewise, if you plonk a long concrete lintel in, or a bit of 4x2 or a steel beam, then they will ask for calcs because that is non-standard and there are no calculations already done and the manufacturers of these have not already designed any of them for given openings
LIkewise, if you plonk a long concrete lintel in, or a bit of 4x2 or a steel beam, then they will ask for calcs because that is non-standard and there are no calculations already done and the manufacturers of these have not already designed any of them for given openings