Origin of Monotype Plantin

Here's something that contests the claim that Monotype Plantin is based on Robert Granjon's 16th century Gros Cicero typeface:

The Monotype Corporation identify [Granjon's] designs as forming the basis for Plantin and Times New Roman, but this is wholly untrue.

from 'ROBERT GRANJON (FRENCH, CA. 1513–1589)' at Mike Parker's Story of Type

Can anyone provide any background or evidence re this claim? Is it regarding the wrong lowercase 'a' and the italics:

In fact most of the letter a’s in this font are wrong-fount characters, and the italic is a later type that has nothing to do with Granjon.

from James Mosley at Granjon's Gros Cicero