In most cases, the completion time is fairly straight-forward, and is calculated using the two dates provided in the reviews (date commissioned/bought and date completed/shipped).
In the case of very vague dates, the best guess is used. In the case of two different sets of dates, such as contacted/commissioned on Y date but paid by Z date, the longer date is chosen if there are 2 months or less in between the two completion times. If there are 3 months or more between the two times, the review is put in two different time categories (ex. “1 – 3 months” and “4 – 6 months” ).
An example of a review placed in two different time categories:
Commissioned Maker in January 2014. Paid fully in February 2015. Received item in January 2016.
In this case, the review would be marked as “12 – 23 Months” and “2+ Years”.
FursuitReview does this as people researching for fursuit completion dates may not consider the maker to be working unless they are fully paid first. This method of sorting is the best compromise.
Additionally, Pre-made items are exempt from the “completion time” categories unless the item took longer than one month to receive. In these cases, the reviews are listed in both the “Pre-made” category and the applicable “Completion Time” category.
Because of this, make sure to read the review and understand the context in which ratings and categorization are applied.