Some customers asked us: “It is October, 2020 now, but why are some of our citations published in 2021? Is it an error?”
It’s not an error. Publications from the “future” are actually common these days. Since many journals have this “early online access” mechanism, we often find papers ahead of its “official” publication date. This is exactly what is happening here.
Let’s give an example:
The paper above has an offical publication date in 2021, but its first online date was 2020/09/19. A link of this paper is here.
Publication date has a fuzzy definition now. It can be the “official (print) publication date”, or the first time it appears online, or the first time it is indexed by major search engine such as Google, Google Scholar, PubMed, etc. In the data we provide to customers, we use the “official (print) publication date”.