It's possible that dragging up an old post to embarrass someone might not be considered a personal attack if the person in question is incapable of embarrassment.
Posts with quotes from and/or links to older messages may be removed when the context of the message is ultimately about another user.
For example, there is rarely a legitimate on-topic reason to reply to a post months or years later asking "so what do you think now?" That makes the post about the other User not about the company.
Occasionally, someone may reply to or cite an older post for reference information about the company. For example, "the PPS was .002 in January 2012." That may be an acceptable use if the context is being used as a reference to what was occurring with the company/stock during that time rather than what the other user was thinking at the time.
Again, the context of how it is being used presently is what matters.