Tusk (25 Years: The Chain) vs. Tusk (Album version)

[TrueFaith77]

For the first time, I played the version of "Tusk" on 25 Years: The Chain back to back with the album version and the version that appears on Very Best of Fleetwood Mac. I had always thought there were slight variations between the three (I chalked it up to transfers to/mixing of the cds); however, this time I noticed that the 25 Years: The Chain version contains a wildly different intro. So... I go home... look at the credit in the liner notes and it simply attributes this to "From the Album Tusk"! It's not listed as an alternate version, or possibly as the version released on radio/as a single (is that was distinguishes the album version from the Very Best of version?).

So what is the true nature of this version on 25 Years: The Chain?