In short there are pages that you can't access by using the page navigation at the bottom.
So for instance if we take a look at the actual last page of
this forum it shows 189 of 167 pages and if you move backwards to a newer page the link for the older one disappears. It seems that the amount of pages missing for any forum section is proportional to the amount of posts in it.
This might not seem like that big of a deal for older forums but for any new forums like the developer one, only showing the first page and not the second might be considered a bigger deal.