The bills with the numbers in black are ok and you will not have a problem. Look at the bill and you will see the following safety marks as a regular Argentine bill. The 'sewn in' metallic strip with the BCRA letters on it. A watermark of Roca's portrait, with the letters JAR -in the black bills the letters are a bit off center, but they are there,- a watermark of six to seven horizontal stripes. If you see those marks the bill is ok and it will be accepted.
I have gotten two fake bills only in my 16 months here... One 50 pesos and one 100 pesos and the work is so shoddy that you can tell it is fake from a mile away. Still, they make for a great souvenir. When you are counting your bills at the cueva count them on the side of the water mark and look at the ink on the 100 number and at the metallic strip. If you don't see the letters or the green ink is too sparkly, It is a fake. If you are a regular, or bring in a lot of cash, they will exchange your bill -after all they want your greens,- BUT given that the operation you are doing there is illegal, just as their business, It is pretending there is honor among thieves. If you get 1 or 2 fake bills it is not that bad.
