BNP would not be obsoleted by BNF or the N-Assay. BNF/N-Assay work by detecting antibodies that specifically bind to certain bacteria. BNP is used to grow bacteria. Two separate applications that complement each other.

For example, BNF/N-Assay detects what the bacteria is (and its antibiotic susceptibility). BNP can then be used to grow the bacteria for other uses.

Perhaps the fact that BNP can be used to detect bacteria is what raised your question about it being obsoleted by BNF/N-Assay? Its true that BNP can also be used to detect bacteria, but the method is different from BNF/N-Assay. BNP grows the bacteria on a membrane which is stained -- the staining is what makes it possible to identify the bacteria.

I'm not sure of all the circumstances under which BNP, BNF or the N-Assay would be used, but all three are independently viable products.