IMHO the much touted embargo has always been a myth. I’ve been in this biz for more than a few years and have worked in different global markets and in all that time, I’ve only ever once issued a release under embargo. That one involved a major international celebrity and, of course, it was broken.
Rule number one of human communication? If you don’t want anyone talking about something, keep it yourself. It’s pretty simple. The same rule holds true for news releases.
Anyone who relies on having embargoes respected it taking a risk. I say play it safe. Give an advance on a story if you like, but you can’t give a journalist a story and ask him not to report it. It’s just disrespectful.