Olmo Rondine David Rapley/Racing Bicycles: 100 years of Steel, pp 100-101.
Google Books Swallow rondine lugs with seat lug side slot; chrome head lugs and fork crown; chrome stay and fork ends; Campagnolo Cambio Corsa dropouts and fork ends BRAZE-ONS: top tube brake cable ORIGINAL PARTS: 4 speed Campagnolo Cambio Corsa; Campagnolo hubs; Nisi 36 hole rims; Magistroni Senior five pin crankset with 48t chainring; Olmo headset; Brooks B17 saddle; Balilla brakes; Silver blue paint DECALS: decal remnant on top of seat tube; otherwise, none DATING: book author says bike is 1948, from an Olmo team mechanic Serial Number 889 1946-1951? ] bg.legendary.bikes/e Bay: may not be an Olmo; seller does not say it is an Olmo in the listing and description; does not have swallow rondine lugs; chrome forks; Campagnolo Cambio Corsa dropouts and fork ends REPAINTED...
This Olmo Serial Number Dating Registry records Olmos with original dated bike parts or provenance, and sometimes only with decals, in order to attempt correlating an Olmo serial number to a year or year range. Absence of a question mark means there is some certainty about a bike's year or a range of years, established by parts dating, provenance, etc., or by preceding or following dated bikes.
Later Olmos with date-able elements are actively added, as well as pre-1978 Olmos. A TIPO RONDINE decal may or may not appear on some older Olmo bikes, and refers to the Agrati AM lugs, with 'rondine' meaning 'swallow.' Some older Olmos have the ornate Agrati lugs which Emilio Bozzi sold as Brianza sportiva lugs; the accompanying Agrati rear dropouts are stamped with a scalloped back.
Olmo [Gran Sport / Professional Regular] Roger Barrett: Swallow rondine lugs with no seat lug side slot.