Yes...you are all correct. The hidden forum to get things setup came first, public forum came later. That was partly because I was very busy back then, and didn't have the time to dedicate to any public threads, so didn't really want a public forum to encourage them. As soon as I got my free time back, we created the public forum and things have been surprisingly successful since then :)
But, we actually have a rather curious mix of threads. For understandable reasons, we only have the SEO for the rare error codes. Common error codes have Google first page dominated by big forums which have been around for years. We are doing better though all the time, but esentially we are still dominated by a lot of repetition of a few exceedingly rare error codes.
It really caught me out when I first came here TBH

I was so used to all of the common error codes, with the very occasionally moderately rare error code, that it was a huge shock to have a flood of rare error codes all of which needed much research. But I am specialising quite nicely in our weird error codes now
Richard