Hello,
It's possible these documents had a Publish from date set in the future or a Publish to date set in the past, which would prevent these documents from showing on the live site even though they were published.
The data shouldn't be lost. Instead it should be saved in a different version than you are currently viewing, unless you deleted the version history for these documents.
Also, can you please let us know which version of Kentico
CMS you are current using?
Best Regards,
Edward Hillard