Look, I know I don’t have anywhere near the largest or best collection on here, but I think it’s really cool that, mostly because of my quirky collecting habits, I’ve found 11 cards in my collection that nobody else here has. They’re all “off brand” vintage cards from pre-1947 of players no one’s heard of. But I love the concept that even mid-range collectors like me can have a nearly unique card. Part of the fun of collecting. I’m so glad I expanded beyond Topps about ten years ago.

Y’all have any “unique” cards? 

My grandson bought me a set of tobacco cards a few years ago.  50 card set and I was only the one that had any of them at the time.

I have one card that would fit this criteria that does not include 1of1 issued cards.  2007 UD Star Signings - Sean Casey (Auto Card). I searched for this card since I found it on the checklist when it was released as it was the last Tiger card I needed from that set. I was beginning to think it didn't exist but would occasionally try to find it on eBay and some of the other sites that offered cards. Well, one night I got up to let my dogs out and while waiting on them to return I searched eBay for the card...using my phone. Boom, one was listed with a buy it now...I snapped it up immediately.  All images on the net, including here and those that have been captured are of the card that I uploaded to TCDB.  As far as I know, no others exist, but if I was guessing it probably has a low production number of 3 to 10 cards in total, some of which are probably in someone's set or long and forgotten box of cards. It was listed as an SP back in the day so who actually knows. The card sits in my display case with the Verlander, Shelton and Bonderman from the same set. (I still occasionally search for this card even though I already have one copy already.) 

@Vvvergeer, did you use a report to find this information?

Nah. I just looked through some of my odd cards and saw the number of how many people reported the card in their collection and how many wantlistings there were. Don’t know if there’s an easier way. 

I looked for over 10 years for a card to finish my 2011 Topps Throwback Phillies teamset..#11 Leaders card with Roy Halladay, Adam Wainwright and Ubaldo Jiminez.  Finally found one online and grabbed it up; was thrilled to have the only one in TCDBland!  Just looked and ‘dayray’ has one now as well!  To the 27 folks who still seek one..don’t give up!!  😋

There are definitely some minor, independent, and summer collegiate league team sets that I have added that no one else has, and some Czech Baseball Extraliga and Eurobaseball cards that I ordered from the Czech Republic. Plenty of cards on my want list that no one has, too.

Sort of.  There are a few cards that I obtained a few copies of.  The only other members with those cards in their collection obtained them from me via a PIF.  I guess if I kept them to myself I could claim some "uniques".

This little baby is one of my faves and is, by its nature, unique...

https://www.tcdb.com/ViewCard.cfm/sid/340711/cid/20159679/2022-Topps-Star-Wars:-The-Book-of-Boba-Fett---Concept-Art-Black-CA-4-With-the-Tusken-Clan

Warning, long explanation.

Topps started the SN Gold parallel set in 2001. I would get one or two of the Royals cards every year, just for grins.  Around 2010 or 2011 I was at a show and came across a dealer that had a box of several hundred of the gold cards. (I think they were 50 cents each.) I picked up all the Royals cards he had and then decided to find the remaining handful of cards to complete the team set. From then on every year I would put together a Gold Royals team set for the base and update set. After a few years I decided to go “back” and get the cards from years past. 
There is a dealer on eBay that specializes in the Topps color parallel cards.  I probably picked up 50+ from him over the years. Once when getting 3 or 4 I noticed he had a 2003 Roberto Hernandez, gold card, #23, listed but it was $10 instead of $1, or $2 like the others. Since I needed it, I sent him a message and asked why that was so expensive.  He told me that for some reason there were 20-25 SN Gold cards in the 2003 Series 1 that were extremely difficult to find. He said that he had been selling the parallel cards for years and some just never showed up among his many contacts and sources. He sent me a list of the numbers, which included the Hernandez. I didn’t keep the list but noticed that card #252, Joe Randa (a Royal) was also on the list. I messaged him back and told him that I would need card #252 and if he ran across that to please let me know. I also put the card on my eBay search/ watch list.
Flash forward to 2023. I had never found a SN Gold #252 and it was the only card I was missing for my gold team sets. A month ago I did my once a month search for the card and discovered that the same dealer had one. I sent him an offer and got it for $30 + shipping. (Just a little more than the TCDb listed price.) The dealer told me that according to his records it was only the 3rd one he had ever sold. 
I happily received the card a couple of weeks ago and added it to my collection. When I did, I noticed that I was the first to list it. (Someday, I promise, I’ll get a scanner and figure out how to submit cards to the site.)
At least until the 2024 Topps Series 1 cards are released, my Gold card sets are finally complete.

For anyone who made it to the end of this, thanks!