User blog comment:IamJakuhoRaikoben/Chapter 498: Gray vs Invel, Review./@comment-2.85.31.8-20160823091256/@comment-7418318-20160823100041

So far it looks like Invel is one of Zeref's direct confidants/advisors and always nearby, so it's hardly surprising that Zeref is more likely to confide in him and/or that Invel is able to pick up snippets of information from time to time that most of the other Shields miss due to being away from Zeref most of the time.