Right now, my team can connect to a revenue goal we set for 2015, which is marked as Achieved. They are doing this by mistake because there is a new 2016 revenue goal they should be connecting to. The Achieved goals shouldn't be showing up in the dropdown for goals for new epics.
Thank you for the request. We currently provide the ability to connect any goal and initiative (epic).
There are a variety of reasons for this, but flexibility is a key reason as we want to ensure that the correct items are available (even if a user is linking previous items).
With that said, there may be improvements which we can make towards the dropdown lists to make it easier to detect which item to link to.
At this time, we will mark this specific request as "unlikely to implement" but will plan to take a closer look at the overall dropdown in the future, for other types of potential improvements which can be made.