It all involves the scripted groups' line of "EvolveFromEntryDate=true" in the campaign, for the groups to start when they are supposed to. In the Single Mission files, you will see that the groups are much closer to the point of the battle, like the player's sub is, so those lines are usually set to "EvolveFromEntryDate=false", because if they were set to "true" in the Single Mission files, then the groups would be gone by the time the player gets there.
With Random Generated Groups (RGG) in the campaign, it just involves getting the "DelayMin=", "DelayMinInterv=" and "SpawnProbability=" (usually 1, 1, 100) lines correct, and in co-ordination with the "GameEntryDate=" and "GameEntryTime=" settings, along with "MaxInst=" (usually 1) and "MaxUnitsCreated=" (however big the group is) settings. This is where lurker excelled, in being able to make an RGG show when he wanted it to. It is also why the Mission Editor (ME) will ruin most of the settings lurker did, in that the ME has its own ideas of what is valid for those RGG settings, and even the regular scripted groups, which makes it frustrating to work with them...
