I am doing a bibliometric research in Web of Science. I made a research one year ago of a topic in Web of Science and I got a known number of results, as well as the percentual of papers per country. So, I performed the same research (obviously inserting the same day/month/year and range that I originally performed before) and I got results close to the former but slightly lower. The percentages I obtained also varied slightly, so I think it is not likely that I made typographical errors in registering the original percentages and number of papers. Also, as I said, the number of papers decreased so the lack of coincidence between the moment of my research and papers to get online in WoS also do not explain this. One possibility would be a paper was the database but further removed because the journal no longer is indexed in WoS, but do you guys know if it is possible?