This is all off the top of my head, without looking at my parts stash (except for the gold Mafacs on the commuter parked next to me in the office0>
The original Competition had stamped lettering, similar in style to the Racer, and shared the same half-hooded lever. Also, these early Competition were not anodized, rather having a plain finish similar to the Racer. Of course, this version of the Competition had the now hard to find "quick release" straddle wire.
The later Competitions were anodized silver or gold. Some of them had tire guides, some did not. All the gold ones I have seen have had the tire guides. The name often was not stamped on many of these; rather, it was placed on a little sticker in a depression on the left side of the brake (as you face it). These stickered brakes were later than than the stamped ones, judging by the bikes I have seen them used on.
The later Competitions also often had better levers--fully hooded, often drilled, and of more substance than those half hooded levers. The gum hooded levers were slighted larger than those with the black hoods. Both had barrel adjustors.
The later ones also sometimes came with a different type of straddle wire. These wires were double balls, similar to that used by Weinmann et al.
Mafac also had the 2000, which appeared the same as the later Competitions. I have both Competions and 2000s, and other than the sticker, I have not noticed any difrence between the two. I cannot recall if there are any stamped Mafac 2000s. If there is a difference between the 2000 and the Competition, I would like to know as I may well be ignorant.
I don't if it helps, but I do believe that there was a lot of just "whatever" at Mafac towards the latter half of the seventies.