FWIW, I agree. Note that very, very few banks actually use "special deposit slips" so you don't have too many potential respondents who can speak from experience. Also, no one has the incentive to hit the books on your behalf as they probably will not use the information again.
My agreement is solely based on the fact that special deposit slips were offered as an aid to banks in identifying checks subject to enhanced availability; e.g. there is nothing on the MICR line of a cashiers check that indicates its a cashiers check. So, if a customer chooses not to use the special deposit slip, he's waived the special treatment it might have afforded him and the item is just another check.
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In this world you must be oh so smart or oh so pleasant. Well, for years I was smart. I recommend pleasant.