Thanks for the compliments @lyleberr @gemmintpokemon @gengaranimal . 
As for the question of the actual thread: in 99 out of 100 cases I just share it. I could keep things for myself, and in some rare cases I do at first, but eventually I’ll just mention it to some people or just share it in an article or thread here on Efour or reddit, even if I could have better keep things for myself since I’m still missing a certain card in my collection.
But in a lot of cases there are other people discovering the same things eventually anyway, even if I do keep it to myself.
To give an example of something I kept to myself (one of the rare cases where I did), but someone else discovered and shared it later on: the Ivy Pikachu reprint from 1998. It is glossy with Keiji Kinebuchi illustrator, but in pictures you usually can’t see the difference between glossy and non-glossy. You can still see differences by looking at the Energy symbols, though. I had already noticed this earlier while I was trying to find this 1998 reprinted card (and I still am looking as we speak unfortunately 
), but hayo noticed and shared the same in the Efour thread. (If anyone sees this card for sale, please lmk asap.)
At the same time though, if KEI hadn’t shared the existence of this card in 2018, I wouldn’t even have known about it. It’s a Pikachu variation that was discovered years after I was already collecting Pikachu cards. If I had known from the beginning seven years ago, I might have already found it by now.
So yeah, even though the chances are pretty high I’m shooting my own ass by sharing all kind of info on cards I don’t even have yet, at the same time if more people are aware of them and look for them, the chances are higher one eventually pops up for sale.
Also, I personally love all these minor variations in cards, like most of the things mentioned by Zach for example: grey 1st edition stamps; no stage Blastoise error; black flame Ninetales; etc., even though a lot of people don’t care too much about these kind of variations.
And I personally share them almost immediately if it’s outside of my own collection goals, especially if I know it’s within the collection goals of someone else (i.e. the Fossil Muk with repeated black ink dot I shared with joponnes the other day for example). But even if it’s within my own collection interests, I usually tend to share things like that rather quickly. Could be stupid in most cases, but I personally think ‘sharing is caring’. 
And by sharing info, other people also help me out in return tbh. @pichufan linked me to those unlimited edition E1 Pikachu auctions almost immediately when they started for example, and I’m happy to say I was able to win the second one, which is currently incoming. Happy to finally have bought this card after collecting Pikachu and searching for it for seven years. And if that auction wasn’t shared with me, I might have missed it (note however that PichuFan wasn’t the only one who shared it; I think I had around ten messages from people who knew I was looking for it 
).
Greetz,
Quuador