staff's meeting have been postponed vs staff's meeting has been postponed

Some examples from the web:

• Now, industry exhibitions and meetings have been postponed and it is predicted that Asia's economic growth may be affected.
• All non-emergent surgeries have been postponed.
• Tonight's meeting has been postponed.
• The application of that debarking requirement has been postponed twice.
• They started 3 hours late; his exam has been postponed to 6 pm.
• Unfortunately the assessment seems to have been postponed.
• No, the trip's been postponed.
• Giannina's appearance has been postponed until tomorrow.
• This sentence's been postponed until further notice.
• All the nonemergent surgerieshave been postponed.
• He said the autopsy has been postponed.
• Australia has, of course, been postponed.
• Now the trial's been postponed who knows how long.
• Actually, it's been postponed until after her rehab.
• The hearing's been postponed now till Wednesday.
• It's been postponed till after tonight's renomination.
• He'll live, but the trial has been postponed.
• - Just say the movie's been postponed.
• The test has been postponed due to weather conditions.
• Which, I'm guessing, has been postponed.

Some examples from the web:

• Tonight's meeting has been postponed.
• All non-emergent surgeries have been postponed.
• The application of that debarking requirement has been postponed twice.
• They started 3 hours late; his exam has been postponed to 6 pm.
• Unfortunately the assessment seems to have been postponed.
• No, the trip's been postponed.
• Giannina's appearance has been postponed until tomorrow.
• This sentence's been postponed until further notice.
• All the nonemergent surgerieshave been postponed.
• He said the autopsy has been postponed.
• Australia has, of course, been postponed.
• Now the trial's been postponed who knows how long.
• Actually, it's been postponed until after her rehab.
• The hearing's been postponed now till Wednesday.
• It's been postponed till after tonight's renomination.
• He'll live, but the trial has been postponed.
• - Just say the movie's been postponed.
• The test has been postponed due to weather conditions.
• Which, I'm guessing, has been postponed.
• We regret to announce that all flights have been postponed.