@Pete, I used the CDBU0503 in 0603 recently, & later wished I hadn't. Based on a Digikey search for equivalents (when ordering, after I'd laid out the PCB sigh), diodes in 0603 seem to be outrageously expensive compared to slightly larger formats like SOT-23, and much fewer in range too.
@All, re: package categorisation:
I've been looking for alternatives to the SI7617DN & SIS412DN power mosfets recently. They're from Vishay Siliconix in what they call "PowerPAK 1212-8", but which in their own words are "...a derivative of PowerPAK SO-8. It utilizes the same packaging technology, maximizing the die area. The bottom of the die attach pad is exposed to provide a direct, low resistance thermal path to the substrate the device is mounted on. The PowerPAK 1212-8 thus translates the benefits of the PowerPAK SO-8 into a smaller package, with the same level of thermal performance."
And yet when you look at these things, and solder these things, they have no prodtruding leads like SO, as far as I'm concerned they're like DFN, and in looking for alts 'DFN' is what I'd 'instinctively' search on, but find nothing.
I know this is not parts.io's fault at all - you've correctly categorised them by what the datasheet says, and yet - in practise/reality - these things are really DFN. And when you scale this conundrum up to thousands of products where presumably a human would need to review the package diagrams & say "yeah, that's really a DFN, not a modified SO", it seems like an insurmountable problem, especially with the way so many new proprietary packages are springing up.