I think that's correct. I think the other difference is that the FAO definition, as Mr. McIsaac just mentioned, didn't include the requirement for long-term legal protection. I think that's another key difference. The IUCN does require that, which is why, for instance, the rockfish conservation areas don't currently qualify as MPAs under the IUCN definition.
On May 11th, 2017. See this statement in context.