in SWIFT (http://en.wikipedia.org/wiki/SWIFT_message_types), MT910 is "Confirmation of Credit" where MT900 is "Confirmation of Debit".
From what I understand from reading the doc, the only difference is Debit v.s. Credit. However, there are two fields "Ordering Customer" and "Intermediary" in MT910 but not in MT900. Can MT900 not have a Ordering Customer or having an Intermediary?
I tried to find an appropriate forum in stackexchange but stackoverflow seems to be the most appropriate one as this message standard is consumed by computer applications that written by developers.
There's an ordering customer and an intermediary in MT910 because the correspondent banking network means the bank that actually credited your account may not be the same as the customer (bank or corporate) who ordered the credit.
On the MT900 it's you who orders the debit of your own account, so you don't need those fields.