From what we have seen with different members, the coil packs break down and misfire because the insulation breaks down.
Now if this happens on one coil, and you identify the offending coil, and you replace it and your engine is back to running perfect, that is good news.
However, these coils breaking down would appear to be age related, rather than event related. That is to say the individual coils did not get a hit or anything catastrophic that could cause breakage, they just wear out.
This would appear to imply that if one goes bad, all the rest are close to the end of their useful life.
Expensive and all as it must be, the long term solution is probably replace all six.
Otherwise you are just tipping around and messing with the problem, and getting frustrated.
Why not buy 3? One of each length. Mark the new ones with a dab of paint. You will be able to troubleshoot all misfires because you have one of each.
If another one goes after that, then you will only have one of the three older ones to replace.
Just a thought.
Joe