As of April 6, 2020:
The number of confirmed planets are different from one website to another simply because what exactly is being counted is different. Each one of these databases has a different criteria for deciding whether an exoplanet is going to be counted or not. To understand the differences between these numbers, you have to ask
- How is an exoplanet defined?
- How solid must the evidence be for the exoplanet to be counted?
- What detection methods are included?
The answers to these questions are usually in the methodology section of the website, or in a dedicated article.
Here are a few examples of differences:
In addition to this, each of these websites might also be updated at different times. For instance, the NASA Expolanet Archive is updated once a week, but exoplanet.eu is updated daily. But other websites might be updated at different times and with different frequencies. Because of this, two websites with the same criteria might still show different numbers.