1/ It appears that when using py(=>2021), this will only search for the publication year of 2021
2/ It appears that when using py(>=2021), this will search for the publication years of 2021 and 2022
3/ It appears that 30 records have publication year of 2020 - however, the >= range searching command also looks at the publication date field which contains the range Oct 2020 - Mar 2021. Whereas the => command will only look at the publication field itself.
The same is also true for py(<=2021) when compared against py(=<2021)
Thus, the search command py(>=2021) is working as designed and will retrieve atricles that have a publication date of 2021 or greater.
However, if using the command py(=>2021), this will only search for articles that have the publication year 2021
The system architecture was designed for range searching by using > and < symbols. However, the = symbol is used as an exact search and thus => is only searching exactly for publication year of 2021
So, recommend that py(>=) or py(<=) is used to ensure a more comprehensive search retrieval.