Some strategies that I've used to find older posts with our local Advanced Search include:

1. Specifying that the results should be sorted (by date) "In ascending order". That means I'll see the 200 oldest hits instead of the 200 newest.

2. Specifying a date range such as "3 months ago (and older)" or "6 months ago (and newer".

3. Requesting results from one forum at a time.