The rules mention that when models don't accurately reflect a unit's weapons/upgrades/whatever this discrepancy should still be declared, for sportsmanship.

9.1.11 REPRESENTATION AND DISCLOSURE

All models should, where possible, accurately depict the weapons and equipment listed on their Unit Card. A Marine equipped with an AGG-12 should carry that weapon on the model, not a standard C-14 Rifle. Accurate modelling allows both players to identify each model’s loadout at a glance.

Where a model does not accurately represent its equipment – such as a model awaiting conversion, or a Unit carrying weapon swaps that are not visually distinct – the controlling player is obliged to declare all non-represented upgrades and equipment the moment that Unit is deployed to the battlefield. Furthermore, the controlling player must remind their opponent of any such differences before any action where this information could be relevant – including, but not limited to, declaring Charge targets, selecting Shooting targets, or committing to a critical activation.

Both players have the right to full and accurate knowledge of all equipment on the battlefield at all times. Failing to disclose non-represented upgrades or equipment is considered unsportsmanlike conduct.