People buy copies from the original Creaotr (Captain_Nemo) on Teespring, Teespring works with Venly in relation to Venly Market and Venly Wallet.
Each Copy you buy is a NFT that you own, imagine it like buying art pieces, but this time its buying the same Art Piece, but multiple. You own one of the copies or what kind of amount you bought.
Each copy you bought either on Crypto or Teespring, is yours.
(Crypto is a own NFT trading and wallet platform, some NFTs are only aviable there and Crypto has nothing to do with Teespring NFT purchase)
Buying on Teespring, will then get your NFT copy send to you in your Venly Wallet, which you can either trade or sell for your own wanted price in the Venly Market, therefore different price tags on each different copy because different people sell to different prices.
If you do not own a Venly Account and its your first time buying a NFT on Teespring, you will get a account made with your own wallet, the Email will be the same as you have registered on Teespring. After that each copy you buy on Teespring (different NFTs) will be sent to the same wallet. The Venly wallet is linked to your Teespring NFT purchases.
The fields are the same, one for 10k is not better than one for 20k, as said, people sell it because they own a copy and can decide the pricing.
These are as said, sold on Teespring, usually in the past for each new nft a threard was made and the link was posted in there by Captain_Nemo.
And NFT is only aviable if people offer for sale to buy. Some copies as said are still in the Wallet of copy holders.
The NFT fields can only be used by copy holders, they were designed that way to ensure clean market