As of Creo (3? 4?) features do not need to reference the first instance of a pattern in order to create a Reference Pattern from them. However, even if a feature doesn't reference the the first instance of a pattern, when you go to make a Reference Pattern from it, its first instance still cannot be excluded (click on/off the black/yellow dots in the pattern definition screen).
As an example, suppose I want to make a part with many pocket cuts in a row. At the bottom of each pocket there is a bolt hole except in the first pocket of the row. I make the row of pockets by patterning the extrude. I then select the surfaces in the second pocket to create a hole. If I reference pattern the hole, there is no way to exclude the hole from being in the first pocket, even though it doesn't reference that pocket at all. See the attached images to illustrate this example. This can be very frustrating for more complicated or much larger patterns, and while there are certainly workarounds, they are not ideal when this should be a built-in option.