I've only done a little with V700 models, but have already encountered multiple "might be a 66" claims regarding at least two bikes for sale with much later VINs than my bike (and spare frame) that seem well documented to be within the 1967 model year bikes. People want their bike to be a $$unicorn. Not much different than the regular similar claims about Ducati singles being much older than the VIN number indicate when compare to known bikes.
The ad states matching engine and frame numbers. Greg's list doesn't include a matching engine and frame number for this bike, just a frame number. Why not? I understood matching frame and engine VINs were not the norm, if they even happened via MG. my bike came with a supposedly normal mismatched engine and frame numbers (looked to be an original bike, not a bitsa) even though the spare frame I have (from a bike parted out in GA several years prior) is much closer in number to the engine I have.
The little amount of reading I have done discussed how difficult things were from 1964-1966 for MG as they went through restructuring, hired Tonti to help move forward, and the factory was leased in March 1967 year to move forward. From Ian Fallon's Moto Guzzi book-

As inconsistent in minor detail as many Italian bikes are when things are running great at a company, it's hard to imagine that a legitimate 1966 V700 produced and released entirely during bankruptcy would be anything like a 1967 V700 produced under new management. The new people were there to fix what didn't work, not continue doing what was wrecking the company.
Just things to consider for a bike that's got a serious asking price..