@Sean
I was thinking the same. So after a few minutes of investigation I found this:
http://liberfloridus.cines.fr/cgi-bin/affich_...10911,33,1
http://liberfloridus.cines.fr/cgi-bin/affich_...10911,33,1
1370s seems to be the decade. (:

Although I don't like to use TOMAR as a historical reference, on page 403 of that book there is a photo of the remains of a coat of plates that looks to be slightly waisted. It has 3 upper chest plates and 5 horizontal plates. The top 2 horizontal plates are angled slightly inward (and look like the might be lightly dished), the middle one is almost neutral, and the bottom 2 are angled outward.
The Stapleton brass shows 16 rows of rivets, but you could obviously apply the same concept to a larger number of plates. (Or perhaps a double row of rivets on 8 plates.)

I think it would not have been uncommon to show people of ancient time as 'old' with the equipment of an earlier generation. I have no doubt that there were men who were armed in this way but there are many MS and other artwork showing markedly different armour than this from this time and earlier. In fact the knights from the taymouth are equipped the same and that is 40 years earlier.

A great example of artists using old armour to show age is the Taymouth Hours. The same MS has men in up to date armour c.1330 and others in various 'older' armours as the murder of Becket. Interestingly the becket murder scene has knights in mroe or less what I'd expect them to have on armour wise.

Text by 1340-1350 is awash with plate/rigid limb armour for the arms so I'd not take this to be a likely scene of a modern king for 1370 as it in my mind is unlikely to counter solid inventories and such for an artists fancy. Just look around at modern art.... we can be in big trouble with future generations if they use that same method for how we looked and dressed, etc.

Jojo,

And we have to be careful assuming the rows of plates did not have more than 1 row of rivets per plate.

RPM

I agree. What I mean is there could be 3-4 rows per plate even or one. We just cannot know for sure without more evidence.

RPM