are individual satoshis as secure as an overall bitcoin? I don't really understand Bitcoins as well as I'd like.  I understand that eventually there will be 21,000,000 bitcoins mined.  And, I understand that each bitcoin can be subdivided into 100,000,000 satoshis.  so there will one day be 2,100 Trillion satoshis in the system.  

So, Is each satoshis as secure as a bitcoin?  Or, I was imagining, that even though each bitcoin might be highly secure, perhaps a bitcoins individual subdivisions might not be accounted for so well.  Suppose one organization had a several bitcoins, but a great many of the organizations members owned various numbers of those bitcoin's satoshis.  Would they need to be extra concerned that their satoshis could somehow disappear, when they owned less than a full bitcoin?  

(Does accountability begin with the satoshis, or with the bitcoin?)
When people "hold Bitcoin", they actually have access to a private key that allows them to sign for one or more unspent transaction outputs (UTXO) of the corresponding Bitcoin sum. The amounts in transaction outputs are in fact specified as a count of satoshis. 

All unspent transaction outputs are tracked by each full node on the network, therefore, it is no more likely that a smaller amount is going to be forgotten rather than a greater amount. However, since transaction fees are paid for transaction size and not transacted amount, smaller amounts can have a much higher relative cost to be spent than larger sums.