Demellion
Since Arma 3 1.42 you can also return a control inside a controls group using controlsGroupCtrl (created with ctrlCreate or inside a controls[] of a control config). Example:
((uiNamespace getVariable "RscUnitInfo") displayCtrl 2303) controlsGroupCtrl 154; // Display -> Controls Group -> Control
Note that control inside controls group having -1 IDC currently cannot be returned in any way.