Not at all, in fact during the pre-XP/Post ratio era there were many threads that extended beyond this. Around the turn of the 14th century this all changed and threads began to take on a longer single post format as opposed to the multiple terser post format of the previous era.

I believe there is even a group that reenacts these old time discussions, though I can't find the link right now ;).

But what is the record number of 'RE:'s for a post with some actual content?

You are reading it now (for certain definitions of the word content).

(I'm not really here anyway)