The existing codes can be checked at http://www.bic-code.org/consultation-of-the-containers-bic-code-register.html.
The BIC Code is targeted at ISO standardized loading units (containers) and the ILU code at non-ISO standardized LU (swap bodies, another continental LE). The B.I.C. code is valid worldwide whereas the ILU code is only valid in Europe (CEN). But as soon as the mode of transport modes is changed via transshipment facilities, the LU has to be marked with one of the codes. No marking is necessary for factory transport. It is also not necessary to use both codes at the same time for labeling. As a rule of thumb: If the LU is directed to reach a seaport as the last station, the BIC code must be used, otherwise the ILU code.
The SGKV will be happy to provide additional information. You can find the B.I.C. at www.bic-code.org. Information on the ILU code is available at www.ilu-code.eu.