I worked out this trick in making the Character Sheet Index in Heaven. The gimmick is to reference the
entire thread, with the intended post number. You can't just refer to the page number, because that's dynamic.
For instance, the link to the page in Heaven's Character Sheet repository, for the Numenera game, reads as follows:
Numenera Character Sheet:
https://rpol.net/display.cgi?gi=2&ti=21&msgpage=&show=all#65
The fields it uses (after the question mark) are:
gi, the Game Index. When you're reading the game, this number shows up in the URL no matter what page you're on.
ti, the Thread Index. This is specific for each thread within the game.
msgpage, the Message Page. You can probably delete this part.
show=all#[post number], the most critical part. It
requires the
show=all flag, even if it's only one page worth of posts. This is a safeguard for when (if) the thread folds over to a new page. Immediately afterward, put in a pound sign and the post number (seen as "msg #5" or the like at the top right of the post).
When someone clicks on the link, it will load up that thread of that game, force it to show the
entire thread, then jump to the specified post.