I'n sure none of the scientific sources every quoted it as a 'comet of a lifetime', just that it had the potential to be so. I can remember back in the 70s when Kahoutek was expected to be the 'comet of the century' too! "Before its close approach, Kohoutek was hyped by the media as the "comet of the century". However, Kohoutek's display was considered a let-down,possibly due to partial disintegration when the comet closely approached the sun prior to its Earth flyby. Since this was probably the comet's first visit to the inner Solar System, it would have still contained large amounts of frozen volatiles since its creation. Although it failed to brighten to levels expected, it was still a naked-eye object. Its greatest visual magnitude was -3, when it was at perihelion, 0.14 AU (21,000,000 km; 13,000,000 mi) from the Sun"