How to search for missing photos within a specific date range.

I am working on a Photo-a-Day project and have recently noticed that my numbers aren't adding up.  I currently only have 318 photos, when I should have 324.  Is there a way to ask Lightroom to show me dates where I had no photos added to the catalogue?  

By @Joe33736770bbcd

Activate the filter bar, select Metadata and set one of the columns to 'Date'. If you did not shoot any photos on a particular day, then that day will not show in the list of dates.

One reason why photos may not seem to add up to the expected number, is because even though those may be in the Catalog, they are not presented within your current Catalog view. For example if some are concealed by stacking, or there is some filter active which is suppressing the display of certain images: by file type, or virtual copy... or, some don't appear in the expected Collection or Smart Collection, or lack a certain expected keyword, or they are not in the expected folder location - or even, the expected drive volume. Personally I would eliminate these possibilities, and rectify any issue of those sorts, before contemplating any Sync Folder or re-importing. That last may easily do more harm than good, especially so far as connecting back to any surviving editing you may have already applied to the same photos.

If these photos are within the Catalog but marked as "not found" on disk (due to some external change), they would still show up normally so far as the above is concerned. Such photos would need to be re-browsed or else the external changes on disk reverted. 

If these photos really are not in the Catalog, then in Library Filter Bar you can show a column for (capture) Date. This breaks down to Year, Month, Day. It only populates this listing with entries that reflect the date of at least one photo, so far as the set you are filtering from. So if your photo-a-day was missing from March 5 and 6, but you had otherwise got every day that month, the column would show March 1 2 3 4 7 8 9...