I'm running photos 1.5. Older versions of Photos used a different date format for the title of moments. Right now most of my pictures are organized using the old date format (YYYY-MM-DD). Is there a way to modify the date format for all moments in the latest version of Photos?
Check your format in System Preferences -> Language & Region -> Advanced... -> Dates and modify there by drag and drop the dates fields as you wish. These correspond to your locale settings. Note the format (YYYY-MM-DD) is not old, it is just the ISO standard today.