Is there anything we can do to search posts by year

You cannot do that directly but this should be possible with a custom template where you allow uses to select the date and time (to-from) with drop-downs in an advanced form

This is the custom template used to display results when seamless mode is off.
https://github.com/WebberZone/better-search/blob/master/templates/template.php

You can create a file called better-search-template.php in your theme’s directory and the plugin will use it to display the results.