Is searching in article references considered a systematic way of literature search?
I would add to the other answer(s) that you could validate the first approach using the second approach. If your search criteria systematically miss relevant articles in the journals covered by the database, then that's a clear sign you need to reformulate your search criteria because they're clearly not sufficient.

The second thing to add is that any search should also try to find unpublished articles. These are definitely not going to be in databases, but may be cited in papers (thus the importance, at least in my view, of the second approach). It might be worth adding a third approach that involves search conference abstracts, where unpublished (especially recent) work is likely to be found.