Answer:
Technically, the rule calls for describing the account type (not the account number), however, it's my personal opinion that providing the account number (or the truncated acct no) gives the consumer more specific info than required, and should be OK. I have never heard of a bank being dinged for including the [truncated] account number in lieu of account type.
So much has changed in the industry regarding EFT processing and statement rendering since Reg E was issued, and nothing has been done to make section 9 a little more workable for the industry and its consumer customers. It's really pathetic in that regard.