If you order your gases to AWS A 5.32 (any edition) the supplier is supposed to label the gas as part of complying to the specification. This labeling is just like the requirement for labeling wire. If the product is to fully meet the standard, each container is to be labeled.
From the specification (2011 edition):
10. Marking
the outside of each cylinder or other container (see 3.4) shall be clearly marked with at least the following information:
name of the manufacturer or supplier;
trade name;
designation in accordance with this Standard (see 5.2);
health and safety warnings in accordance with local, national, and regional standards and regulations as required.
Al's specifications above are from the 1997 R2007 edition. The new standard has different impurity limits It turns out that if the Referencing code (D1.1, for example) specifies a document by date or edition, you are to use that version. If the Referencing code used an undated reference, you are to use the most current version of the specified document. Of course, the Contract can change this requirement.
for Milton G, 3PPM moisture corresponds to -92F dewpoint. There will also be tolerances on the accuracy of the mixture, for a 75/25 (either edition) it wil be +/- 2.5% from the nominal 25%, or 22.5% to 27.5%, assuming the gas is to meet A5.32 requirements. Finally, current (2011) purity is 99.99% global purity, and a maximum of 40 PPM H20 on "I" classifications, which covers argon, helium, and argon/helium mixes.