Is email suspend older than 24 hours truly deliverable?

All newsletter subscribers from the same company (different locations) are marked as email suspend = true, cause is 554 5.4.5 closing connection, and timestamps range from July 2019-today.

After reviewing this Community thread, I know that it's recommended to stagger the sends to prevent future suspends. However, 90% of the subscribers were last suspended more than 24 hours ago and are showing recent emails delivered.

• Are these delivered emails in activity log truly delivered? Because not one of the subscribers has opened an email in past 90 days.
• How are other Marketo users staggering newsletter sends to avoid email suspend and improve company-wide deliverability?