What gets me with CNG auctions, they had a lot of coins from the "Continental Collection" Rauch Auctions. CNG graded all these coins as EF/ Rauch had most graded as "stempelglanz"=mintstate! Rauch grade very conservatively. Even more fascinating, a lot of Heritage ancients slabbed as MS-CH/ MS-GEM were in previous Ars Classica/ CNG as EF! CNG rarely ever grades a coin FDC!
I believe this is a trend of some more traditional numismatic houses. A F or VF currency at Jean Elsen, for example, can be easily sold elsewhere like VF or EF respectively. I don't know if this is a way to try to show more caution and thereby to value the service provided, or if this is just a matter of meticulousness. The matter of fact that there are some traditional numismatic houses that are not too much in this context. Who knows...