I just sent a character to a certain place and the character was able to sell me stuff. I didn't buy all the diagrams, but I imagine that kind of stuff can be bought or found in other places.

Are there any instances where you NEED to buy up certain stuff from a vendor before they become unavailable or can you always do it later?

The Innkeeper in White Orchard sells you cards that you can't get later. That's the only one I know for sure.

I apparently missed a rare card from the Baron in Velen after finishing that quest line. I haven't noticed any important equipment or diagrams you could miss, but it's possible.

The devs at CD Projeckt Red said they are going to patch in another Innkeeper at the White Orchard inn so you can get those cards if you missed them. I'm concerned about Gwent cards because so far they're like finding a needle in a stack of needles what with certain cards being randomly won from certain NPC's. I can't wait to read the gamefaq for this one when it eventually comes out. Stringent is the best word for all this damn collecting.

I believe I did buy up all her cards before she became unavailable. The NPC's only give a single card each right? I imagine it has to be set or else how would you get unique cards that can only be given by an NPC?

Apparently the Crow Crystal Skull that's in the opening cinematic can be picked up near the very first starting area in the game. I have been told it also disappears if you don't pick it up before completing the Gryphon fight.

WHAT

It also ends up in the "quest items" section of the inventory, worryingly...

@zeik: You should have gotten a notice in the questlog that says to play someone else now. That guy has the baron's card.

From what I've read of the guide, you can't miss anything important. If its important, its moved to a merchant. Or in the case of gwent cards, another player.

Man, I don't know how you all have enough money to waste on Gwent cards. I have enough to keep my repairs and gear current and that's about it. Also, I have zero clue as to where to even start if I wanted to start with gwent.

There's a guy playing at one of the tables in the White Orchard Inn the first time you go there (when you ask around to see if anyone has seen Yenn). He gives you a game / tutorial. You can probably just watch the tutorial on youtube if you missed it, it's a pretty simple game to get to grips with.

@jimbo: Oh, i got that far but outside the tutorial haven't played any or bought any cards.

Ah. Well it's worth a look I think. You do start off with one full deck which is plenty good enough for the first few players you'll find.

There are times when you beat a boss and the cutscene gives you a choice between sticking around and instancing to another area. If you choose to stay, you can often loot the boss room for stuff. Example: When you go to Bald Mountain and defeat Imlerith, you can loot a Magic Acorn from his body. When consumed, gives you +2 ability points.

You can only get one card from beating NPCs, yes. They don't all give you specfic cards, though. Many of them are random.