Yes, it would appear the forum tolerates my adding of information.
"SMF does not have an official rule that outright bans necroposting (we tolerate it up to a certain point)"
and later:
"-Guideline in regards to statement '7c' from above (necroposting to add a new bit of helpful wisdom): This is one of the times where a necropost might be worth the risk of attracting any potential ire, depending on the level of helpfulness, accuracy, and/or relevance of your words of wisdom. If you are ever in doubt, though, as to whether you should necropost your words of wisdom in the old thread, or rather introduce them in a new thread with a link pointing to the old thread, just let it be said that no one will ever fault you for doing the latter of the two."
So, to clarify, I was never in doubt this was a useful piece of information.