Any time a web site or webpage is "not found" or the contents appear to have been changed and no longer contain the information one is seeking, it is a good idea to check the WayBack Machine, Internet Archive: https://web.archive.org/

The WayBack Machine reports that this partcular link (https://www.davidsongifted.org/search-database/entry/a10421) was saved 10 times between July 2, 2016 and February 25, 2021.

https://web.archive.org/web/20210225113845/https://www.davidsongifted.org/search-database/entry/a10421