the yellow gold would have been marked 140.1.89, as JLC's codification is VERY EASY to understand:
First 3 digits are the watch reference
4th digit is the case material (1=yellow gold, 2=rose, 3=white gold, 5=steel/18kt yellow gold, 7=yellow/rose gold, 8=steel)
5th digit is the band (same as above, but adds 4 for leather with deployant buckle, 5=pin buckle)
6th digit is the dial color (0=white, 1=champagne, 2=silver or light gray, 3=ivory, 4=dark gray [like the Reverso shadow], 5=brown or red, 6=blue, 7=black, 8=black opal, 9=jeweled dial
7th digit is for specialties about the dial (A=English calendar, D=Deutsch, F=French, E=Emerald-set, R=Ruby-set, etc.)
-Dean