Document EVERYTHING and make sure you have kept detailed notes of your search process:
Databases searched and platforms used
Keywords, phrases, controlled vocabulary
Filters used (i.e. date limits, publication types)
Date of each search
Number of articles retrieved at each step
Standards and Recommendations for Search Documentation
The IOM refers to documentation in a few sections of its standards. Nested in section 2.6 on developing a systematic review is a standard that states describe the search strategy for identifying relevant literature. In section 3.4, the IOM recommends that a line-by-line description of the search be included, with dates of searches in all databases. Section 5.1 identifies 14 required elements for reporting systematic reviews, the most relevant of which state that descriptions of databases and other information resources used to identify relevant studies be included, as well as the search strategy.
PRISMA PRISMA has a 27 point checklist that outlines reporting recommendations. Items 7 and 8 on the 27 point checklist are directly related to search documentation. The two combined tell you exactly what to document: the databases you searched, when you searched them, any additional sources of information, and that you should present the full strategy used in at least one database.
The Cochrane Collaboration
The Cochrane Collaboration does the same thing in a slightly different way as described in Section 6.6 of Part 2 in the Cochrane Handbook for Systematic Reviews of Interventions. Like PRISMA, Cochrane recommends that you document all of the databases you search, the period you searched and the date of the last search, any limits or restrictions on your search (like language or publication types) and any individuals or organizations you contacted. They also recommend that you include the full searches of all databases as an appendix to a published article. They also state that strategies should be copied and pasted, not typed, to avoid transcription errors.