I have a UK 2011 model R35 (DBA).
The gearbox was replaced under warranty at the beginning of 2014.
My experience would seem to support your opinion.
The NHPC who replaced the transmission commented that they believed the new transmission supplied by Nissan was a new model due to it having a different part number to those listed for earlier models.
The service department was unable to give me any more information about any differences between earlier models of GR6 and the current version.