Database content constantly changes and records are added retrospectively so years of coverage are fluid.
It is important to understand that the years indicated in a database name – such as Ovid MEDLINE(R) ALL <1946 to present> often refer to the date the catalogue started (1946 in this case) and not to the date of the earliest publications indexed in the database, which in Medline go back to the late 1700s.
For many bibliographic databases it is not possible to accurately define the years of coverage. That is why we keep these records for systematic reviews:
Years of coverage are constantly changing in most databases, and old publications are often added retrospectively. This is the best indication of coverage that we have been able to research, as at August 2021.
Ovid Medline ALL
APA PsycINFO (Ovid)