You're down here in my home town? Hope you're enjoying the rotten weather.
Those three are a kind of traditional fixed blade pattern that we call "puñal criollo" (following the terminology proposed by local collector and writer Abel Domenech). They are what you'll typically find at a tourist spot like the Feria de Mataderos. Some of those blade work surprisingly well, though. Most of our knife industry is located in Tandil (south of the Buenos Aires province), and got started around WWII when imported blades became hard to get. Nowadays they use whatever carbon steel they can lay their hands on, so quality is a bit hit or miss. Most people here use this type of knife as personal steak knives for "asados", rural work knives tend to be larger but of similar design (with wood or stag handles most of the time, silver for showing off).
The knife marked RDM was made by Roberto de María, from José C. Paz (Buenos Aires province). I've seen some interesting stuff from him, he uses mostly 1070 and 5160. I haven't used any of his knives.
If you're still here and you can read Spanish, try to get a copy of "Dagas de Plata" by Abel Domenech, a fantastic book on Argentine knives with lots of photos (the best one, in my opinion). We've got excellent, very talented bladesmiths in Buenos Aires, if you're interested in meeting some of them I can send you a couple of phone numbers and e-mail addresses. Oh, and if you've got the chance, visit the town of San Antonio de Areco. It's close to Buenos Aires and there are lots of tradional silversmiths there that make beautiful stuff (lots and lots of knives!), and other activities mostly centred on recreating "gaucho" culture.
Let me know if you need any info from a local.