well Tzeentch is the Lord of Change..lol

I think it might be a display issue: Technically at that point you have two potential ward saves; the ToP and the parry (shield) save. Depending on the logic/sorting, it could well be showing one in favour of the other (in this case the parry) and also failing to account for the MoT because it's weird.

Chaos Knights of Tzeentch
 

when I take Chaos Knights of Tzeentch and add the Blasted Standard the ward save does not adjust to 4+

Kazyk the Befouled and Kazyk's rot knights are not available

Also, Chaos War Mammoths were reduced to 550 points as of Tamurkhan, and they can now take marks of chaos, a howdah (which would take it back up to the 600) and/or a warshrine.

See answer in Chaos Deamon thread.

The cost for an enchanted shield (15 pts) is at odds with the cost in the Hard cover rule book (p502, 5 pts)

Not a bug. Please check all relevant rules updates and errata before reporting bugs.

I did spend time looking around for which value to use including other peoples army list but obviously I've missed something and will have to look more in the absence of a link/reference to help me understand it.

in the main Rulebook (somewhere under common magical items) is stated that the costs in Army Book have precedence above the costs referred in the main rule book.

Similar problem, but the sword of striking is using the main rulebook cost (15pts) over the armybook cost (30pts).