It is common to find small amounts of elements in an alloy such as 304 stainless steel that are not listed in the specification. This is due to the use of scrap as one of the raw materials for stainless steel, which is the industry practice. How much unlisted material is allowed depends on the specific product form and standard specification used. Generally, unlisted elements cannot be at level high enough that would cause the alloy to "become a different alloy" or not meet other specifications like tensile strength, etc. The copper numbers seem a bit high but are unlikely to affect the performance of the 304 stainless steel in your application. To be more certain, you could always have some corrosion testing done on samples of this particular 304 stainless steel.