Sampled data sets are based on routes (origin-destination pairs) taken as a subset of a global data set.
The sampling mechanism is based on the market field and not the user location. At Skyscanner we define a market based on the website e.g. Skyscanner.com.sg = SG market.
We don't keep a historical record of the sample sizes. This means that if we re-run a sampled report for our partner(s), the sample size is changed. Even older partners for the older dates will be using the new sample sizes when the report is regenerated.