My guess is that when VS moved the forum to the VBulletin platform, they relied too much on older VBulletin tools they'd typically use to update things like link structures in embedded content. If so, that's unfortunate. A developer well versed in such migrations could have put together one or more scripts that checked those embedded links in the database itself for proper structure, using search and replace patterns designed to address them globally. Doing so would have also minimized issues like the one associated with broken images hosted on OCN, by provisioning for changes to image srcs (the URL of an image) as well. That is, as long as the names of the image files didn't change as a result of the migration.
For instance, an overly-simplified example of two links follows, one of which currently works, and one that doesn't:
working link: https://www.overclock.net/forum/61-water-cooling/411797-block-flow-rates-martin.html#post4904052
broken link: https://www.overclock.net/water-cooling/407027-last-one-my-q6600-cpu-waterblock.html
Given the examples above, using the proper tools and/or correct custom scripting, overclock.net/water-cooling/
in the broken link would have been replaced with overclock.net/forum/61-water-cooling/
everywhere, resulting in the correct path to that page in this instance:
Naturally, with respect to the new forum structure (as well as the non-forum content included in OCN's standalone pages), you'd have to account for all variations in your script(s). That includes any changes that might be necessary as far as (e.g.) permalinks to single post pages are concerned; and/or any links that might be dynamically built.
All that said, I won't comment on how long all of that might have taken though, at least not at this point in time and in a definitive way, because a review of the new site's structure would have to be accomplished first to ensure a comprehensive fix.
Certainly not more than the seven months it's already been though.