Yes, but obviously they don’t, and legally the definitions are blurry.
Honda at least differentiates between marketing material from their sales department and marketing material from their maintenance department (which they don’t consider marketing).
Where I am at least, their automated texts come with a link to manage the messaging you want to see from them, with options to choose exactly which types of messages (if any) you want to see.
It the 'legitimate business' catch. In this instance I'd imagine it's a time based message based off of purchase. And as you said, highly likely from different departments that keep separate DNC lists
Not really. If they schedule oil changes every 6 months the mileage check is to see if they should also schedule like a transmission check so you don't have to keep coming back
Services are determined by mileage. If they don't have your mileage they're just marketing services to you same as if Jiffy Lube started spamming every customer number telling them to come in for an oil change.