The 13-D I assume you mean TYII, right? If not, well, it didn't need to be treated, and our bad for not mentioning this beforehand. I'm glad you're keeping an eye on instead of letting them sit; you're learning something. Good luck with the others!
Picture Time! Okay, so before: https://www.flickr.com/photos/131737095@N02/23414004940/in/dateposted-public/ After: https://www.flickr.com/photos/131737095@N02/23601136922/in/dateposted-public/ kinda hard to see... Top Right: 1917 Top Left: 1914 D Bottom Right: 1922 Bottom Left: 1927 D 1913 D (I'm sorry, the dates are very hard to see. I sure hope the date didn't worsen in the solution, i kept it in for an hour after i saw the 1913, possible damage or paranoia?) Front: https://www.flickr.com/photos/131737095@N02/23081546804/in/dateposted-public/ Back: https://www.flickr.com/photos/131737095@N02/23627174361/in/dateposted-public/ Photos from an hour before: (You can see 1913 better) https://www.flickr.com/photos/131737095@N02/23683609976/in/dateposted-public/ https://www.flickr.com/photos/131737095@N02/23081541844/in/dateposted-public/
It may end up a details coin, but which would you rather have, a details coin WITH a date, or a dateless slick?
There are a few years which can be definitively dated by certain aspects of the hair ribbons, even if the date isn't visible. No acid bath or Nic-A-Date required. That doesn't really change their cull status but it could help when looking for varieties. 1920, 1921, 1924 1925 (something I noticed while sorting through thousands of Buffs amassed by my grandfather)