Here's my concern with adding any missing ink, missing foil, mis-printed, etc. cards on here as variations. Actually, I have a couple. And some additional thoughts for fun.
1) Literally every card from 1987-1992 could probably have an ink variation. Whether it's a random dot, faded ink, whatever, there would be many, many cards (in some cases, I would imagine entire sets) with this issue. Not to mention, as time goes on, and these cards get older, they can start to fade. So something that wasn't a variation in 1989 now is in 2018 because the ink has faded away? That wouldn't make sense to me.
2) Re: adding to the database if enough in existance can be confirmed. How do we determine how many or a certain percentage of cards have the missing ink/foil, whatever variation? We are a small sample size of the hobby as a whole. Do we take site membership percentage? If 51% say that hey, my 1991 Topps Benito Santiago has a random pink dot on the lower right corner, is that enough to consider it a variation? Do we go to COMC, eBay, other sites and factor those numbers in as well? That doesn't seem practical or necessary to me.
3) If I'm a collector and I see that there's 37 ink variations of a 1988 Ozzie Smith Donruss card, I'm going to take two courses of action: either say "forget that" and never bother looking for them (possible) or I'm going to spend years searching for common cards that might have missing ink or an extra dab of it here or there (including some possible ghost cards because only x amount of our members had it but we added it as a variation because there it was)
4) Just because other sites catalog something, doesn't mean we have to or even should. Just because Panini lists their checklists with made up numbers instead of the letters used doesn't mean we should or have to use that system. Just because Beckett chooses to list a minute variation does not mean TCDB should or has to. We all do things differently; heck, I catalog my collection differently than here (Fleer Ultra goes after Fleer Tradition, not before Upper Deck). My point here is that using what other sites do is not necessarily the way we have to go about it.
5) I understand that we all have different collecting interests, and that's great. That's part of the hobby. But this database will not make everyone happy in that sense. We all have things we don't like, whether it's the documentation (or lack thereof), the forums, the way things are listed, the card numbering rules, whatever. It just won't be perfect. However, I do believe Admin has entered a way for us around this problem. By setting up a collection for errors/variation, or even using your main collection, you can do a detailed add and in the "Comments" box, say whatever you want to, including "Missing ink on back", "Foil missing on front", whatever you want! At this point, I'd say this is Admin's work-around for the situation.
6) Finally, vrooomed mentioned this on another forum post on this topic. We have had this discussion multiple times on printing errors and what should and shouldn't be catalogued here. At this point, I think the community as a whole is stuck at what exactly constitutes a printing error vs. a regular error. And I understand that confusion. I think that as long as there is a gray area on what ink/foil/printing/picture/name/number/everything else variations are allowed to be documented here, there will continue to be discussions like this. Not that they're bad discussions, but it's becoming clear that there is just something missing in a lot of people's understanding (including mine; I wasn't aware that the Frank Thomas No-Name card was documented here - it would seem to me that that's a very famous example of a mis-printed card that shouldn't be documented on here [although if the reason behind that documentation is that it is a very famous example, fair enough - after all, Admin's world, we're just living in it]).
Hopefully that makes sense and I didn't come across as rude or mean. Those are just some of my honest thoughts on this topic. Thanks for reading my rambling, if you've made it this far.
*Steps off of soapbox, hoping to never return*
Edit for grammar/spelling
I'll never quit collecting entirely, but I am downsizing. Check out my COMC store and help me thin out what I don't want so I can buy cards that I do want. See something you like? Send me a message on here, and we can knock the price down quite a bit. I'll even take a bit of a loss if it means getting you a card you really want.