Hi Millymoo,
First of all don't panic! It's not big deal.
I started my lit review by describing how I selected the studies (systematic review). Among the criteria was year of publication (example from 2002 to 2012, last decade), then databases I searched in (targeted specific journals or databases like Sciencedirect) and categories (three categories: penguins, ice cream, publication).
If you are really worried, you can put down a page with your criteria just in case.