Hi thank you for your long explanation but you did not answer a simple question.
What does the bracketed value mean under the Credit for Auto exchange mean?
( as opposed to the one under the SAME column that is not in brackets? )
unconfirmed
Immature coins. Every cc has one. When a block is found, newly created coins have a maturation period (wallets call them "unconfirmed") which means they cannot be moved (spent) until a certain number of blocks have passed. This number varies coin by coin. For example, Sia takes around 24 hours to allow newly created coins to be spent which is one of the longest (or slowest if you will).
The reason for such feature is to allow time for the network to evaluate blocks to discover orphaned ones thus preventing double spends.