Nintendo's process for verifying software that gets submitted to their licensing department, called lotcheck, is where completed builds of games are sent to be tested against guidelines that ensure they function and follow Nintendo's set restrictions. Many times games that go through the lotcheck process might end up never releasing, either due to change of plans by the publishers or a variety of other reasons. Localizations and revisions of games also go through lotcheck, but are halted before they reach manufacturing.
It is important to remember that lotcheck will only contain completed builds of games, as the process doesn't deal with games until they are in a final state that the developers believe is ready for retail.
As part of the 2020 Nintendo leaks, a number of lotcheck databases have leaked and uncovered numerous unreleased games and revisions. Currently, lotchecks for NES / Famicom, Famicom Disk System, and Game Boy / Game Boy Color have leaked.