Units in dedicated transports - secrecy or not?

[ebolus]

Under ”A note on secrecy” on page 92 in the BBB it says “… always make clear to your opponent which squads are embarked in which transport vehicle.”

In our gaming group a friendly player says the rule (if it is a rule) states that this is optional. He wants to keep this a secret, which is fine for me – because the runes on his transports all clearly indicate which unit is inside. (My problem is remembering the difference…)

Personally I believe GWs intention is that players must (not should) always reveal the “contents” of each transport vehicle, unless both players agree on mutual secrecy (as the last sentence in the paragraph says).

What do you think?

This is the full text under A note on secrecy:
"To keep things fair, you should always allow your opponent to read your force roster after a game. In the same spirit, always make clear to your opponent which squads are embarked in which transport vehicle. However, before starting to deploy their armies, it is a good idea for players to agree whether or not they can read the opponent's force roster before and during the game. Some players prefer full disclosure (which is the norm in tournaments, for example), as they want to concentrate on outmanoeuvring the enemy rather than springing a secret trump card on them. Others prefer to leave a feel of secrecy around their lists, as bluffing can make a game really entertaining. The choice is yours!"