For the free trial, Review Central will download product reviews from the past 90 days and/or the first 10 pages from the product review page for the Amazon listing. Please remember to expend the day range of the Review filter.
Since you download the reviews base of page, sometime a old review is under the same page with the newer reviews then the older review will also be downloaded. For example, at the 5th page the 2nd review is from 30 days ago and the 7th review could be from 180 days ago. Both reviews will be downloaded as all review under the acceptable page will be downloaded.
Note: Review Central free trial will only download product reviews for the 250 most recently added listings.