Earlier Stronglight 49D crankarms had "Stronglight Depose" in two lines on the crankarms, and later crankarms had "Stronglight Marque Deposee" in three lines on the crankarms. Older crankarms have narrower fluting than later crankarms. Later crankarms are chunkier, more boxy in profile. Later crankarms have both the size and pedal threading marked on the arm as well as "Made in France" and "Modele Deposee" and a date code on the crankarm head where it fits onto the axle. Older crankarms have the crankarm length and "Made in France" marked on the crankarm head, and nothing on the crankarm, sometimes only the crankarm length on the head. There are also differences in chainring bolts and chainring markings.  

This is a 50.4 BCD crank set, meaning that all of the "spider" is part of the large chain ring.  Because of this, many different chain ring styles can and were used on the 49D arms.  Smaller ring is an 86mm BCD. Also can be configured as a triple ring setup.  Crank arms with and without the word 'Marque' have been seen, even on the same bike!