OCB vs ZIP Modified Column Oddity

I notice that several folders in a Directory Opus backup (OCB file) do not display a modified date whereas a ZIP file created (by DOpus) from the same Directory Opus structure shows modified dates for all folders. See comparisons below. Not an issue, just an observation.

It's because the folders don't have explicit entries inside the OCB. It's optional with the zip format, and would just use a little extra space for no real reason in a OCB file.