please consider the following example:
* I bought 10 BCs from ten different people. The ten necessary transactions are scattered through the blockchain (I bought some bitcoins years ago, some just days ago).
* Now I spend the ten BCs and send them to a new owner
I am wondering how the ownership of the ten coins are verified by the nodes. Are there lookup tables for each account implemented, so all nodes just know that my account owns 10 BCs. Or do they look for the ten different transactions in the whole blockchain and search the history? (It certainly could be done both ways, but which one is actually used in current implementations?)
Now, what happens, when I received the 10 BCs with 10 different adresses? Does my client know, that it has to create ten transactions with ten different signatures to get the 10 BCs to the new owner? Or can the 10 BCs be combined somehow?
Thanks for your help!