One of the more surprising things about Go is that you don't need to name interfaces at all. This:

    func f1(r io.Reader) {}

Is the same as:

    func f2(r interface{ Read([]byte) (int, error) }) {}

In fact this is super common, with the empty interface:

    func f3(r interface{})

But somehow the ramifications of that don't sink in and we fail to generalize the principle.

One practical usage:

    li, _ := net.Listen("tcp", ":9000")
    for {
        conn, err := li.Accept()
        if err != nil {
            if err, ok := err.(interface {
                Temporary() bool
            }); ok && err.Temporary() {
                time.Sleep(time.Second)
                continue
            } else {
                panic(err)
            }
        }
    }

This takes a bare interface and checks to see if it supports the "Temporary() bool" interface (which all net errors do). When paired with a type switch this makes for very interesting behavior:

		switch err := err.(type) {
		case nil:
		case interface{ Temporary() bool }:
			if err.Temporary() {
				time.Sleep(time.Second)
				continue
			}
			panic(err)
		default:
			panic(err)
		}

https://play.golang.org/p/J66vaIBGrs2

All that to say, creating duplicate interfaces is perfectly fine.

Should probably name them - makes it readable. But you are correct - duplicate interfaces are fine