Question on ADR and IMDG for sea container (tank container)

Hello everybody, I have a problem. There are goods of class 9 (UN no. 3082) which are only dangerous in road transport (ADR) or ONLY in sea transport (IMDG). As a result, in sea container transport vehicles and containers are marked contradictoryly. This is then a transport according to sub-section 1.1.4.2.1 of the ADR For goods which are ADR but not IMDG, the situation is clear: – Tank container is NOT labeled – on the vehicle is front and rear respectively a neutral warning panel -written instructions (accident notes) are given -a DGD (Dangerous Goods Declaration) is not required For goods that are not ADR, but IMDG, FAST is all clear: -tank container is labeled -written instructions are NOT required -a DGD is required Only what about the warning panels on the vehicle? Some companies say they have to be opened (German Infineum in Cologne), others say no (among others Bayer Leverkusen) and the Marl chemical park). I claim that I can allow the plates, because it is not an ADR. I don’t even need an ADR certificate for such products and the vehicle also no ADR equipment. Who knows exactly??? Greeting Christian