Should catalog numbers include the institution code or collection code?

[zygoballus]

My institution code is CMNH (for Carnegie Museum of Natural History) and my collection code is IZ (for invertebrate zoology). So far, I've been entering my catalog numbers as e.g. "CMNH-IZ-1", "CMNH-IZ-2", but I noticed that some other collections only include the collection code in their catalog numbers, or neither the institution code nor the collection code. And some include both like I do. Is there any best practice in this regard? Is it good to use a globally unique catalog number in the field or is it superfluous to include the institution code and collection code? The Darwin Core documentation just says "An identifier (preferably unique) for the record within the data set or collection."

[zygoballus]

Any opinions are welcome!