Is it possible to see the counterpart sign (nimitta) with eyes open? As a beginner, I practice two forms of meditation: one focusing on the breath (typically with eyes closed), and one focusing on a colored disc (kasina), obviously with eyes open (unless cultivating the after-image). All descriptions I have seen for the former describe the arising of the counterpart sign when the eyes are closed. However, from what I have read on kasina meditation, the counterpart sign seems to arise with the eyes open. I have not experienced either of these myself (and in fact, this link dismisses its importance altogether), so I would like to ask: is it possible for nimitta to form iin either case?
The proof of the pudding is in the eating, no matter how many books are written about the pudding. Once eaten there can be no mistake about it.

As a samatha meditator, both the signs exist for both types of meditation and which still appear when the eyes are open if they are vivid.

Having said that I've quiet a few  fellow  meditators who do not see the signs but continue to develop Jhanas using feeling.