Interesting, thank you. Never having looked it up, I've generally read it as "retroactively conceived." I.e. the PTB decided later that they would rewrite established history.
Won't dive into the hornet's nest of the main topic, except to comment that in the 8 years or so I've been back collecting, I noticed a large increase in the value of Hulk 180 as a percentage of 181. I've assumed mainly that this was because of the huge run ups we've seen in prices (can't afford a 181 so buy this other one), but maybe the persistent argument of "well, 180 is technically Wolv's first appearance" has gained traction.
So for all those with stockpiles of the "lesser" counterparts to a key book, keep it up! Ya never know.