But if the number is cast into the BB shell (as seems likely) then it's a prescriptive, rather than a descriptive. It only means this lug was meant for use on a 60 cm frame. A 58 cm frame could use the same BB shell but would have a relatively shorter top tube.
Another issue with cast bb shell things is that sometimes the years were cast in advance, yet the shell was used in another year due to changes in market demand in relation to the initially planned production. Also, Gazelle for instance sold off their stock bb's with date codes to independent builders when they quit building steel frames.