The more recent one has been validly suggested as a duplicate of the older, and is likely to get marked as such. However, each of the questions has some useful different answers.
If the new question gets closed in favour of the old one people are likely to jump to that older one. And, of course, vice versa. I should point out I have provided an answer on the newer question - not having known at the time there was a duplicate.
Can and/or should these questions be merged? Or do I wait until the new one is closed and then repost my own answer against the old but open question?
What's etiquette in this kind of situation (and perhaps more importantly, what's the most useful/appropriate way of offering an answer that will get seen)?