While reputation of a node is one indicator of how useful a node might be, it is not the only indicator, nor is it necessarily accurate at the time. Sometimes the node may not be read by someone it is useful until much, much later, or someone may not immediately vote on a node because they don't find it useful until later.
As to your question regarding how best to answer, my only advice is to answer as best you can. A quote from one of my favorite movies is, "Anyone who falls flat on their face is at least moving in the right direction -- forward." (Citation can be found in this node.) An attempt at an answer may at least bring up a point or a perspective that wasn't thought of earlier, in the spirit of TIMTOWTDI. I have at times in my own responses suggested what I thought to be a portion of an answer, but was unsure of a complete answer, in hopes of learning more myself while still trying to be helpful.
As an aside, my compliments to johnirl for thanking you for your response. Sometimes we (or at least I do) find ourselves too busy to immediately respond back in thanks, even though the help is very appreciated, then later, when we have the time, so much has occurred that we forget to do so.