I reported this for PTS before but tooltip still says 17% on live where it should be 18%. So I tested again on live to see if there are any changes.
BUG: Shadow mundus with legendary divines trait should give 1% increased critical damage for each armor part and should get 18% total value. However it seems to lower down the tooltip values by 1% and says 17%.
Importance of this is people already got used to not improve body armor pieces to legendary since it didnt increase the old shadow mundus value. And they may think it still the same since tooltip says 17% even if you have 7x purple body pieces. However this is not true anymore. You get extra 1% from Shadow Mundus if you have 7 legendary divines trait gear.
(All screenshots and damage tests are on live)

No Divines : 11%
1 x Divines: 12%
2 x Divines: 12%
3 x Divines: 13%
4 x Divines: 14%
5 x Divines: 15%
6 x Divines: 16%
7 x Divines: 17%
Calculations:
1 x Legendary Divines trait gives 9.1% boost to mundus stone buff.
1 x Epic Divines trait gives 8.1% boost to mundus stone buff.
7 x 9.1% = 63.7%
6 x 9.1% + 1 x 8.1% = 62.7%
6 x 9.1% = 54.6%
Shadow Mundus gives 11% critical damage increase so:
with 7 legendary divines
11 x 1.637 =
18.007%
with 6 legendary and 1 epic divines
11 x 1.627 =
17.897%
with 6 legendart divines and 1 Infused
11 x 1.546 =
17.006%
Since ESO likes to lower down numbers they should give 18% and 17% damage respectively. But it says 17% on the character tooltip for first two cases. And it says 16% if you use 1 infused.
Damage Tests:
I have these below modifiers to my crit damage. I tested on necromancer with no minor force buff. I also removed my bloodthirsty jewelry to get constant damages.
Base Crit Damage (CD) + Shadow Mundus + Elfborn CP = Total Crit Damage
With 7 legendary divines trait I should get,
50% + 18% + 20% = 88%
Calculation:
8001 x 1.88 = 15041.88
Since ESO lowers down decimals 15041 damage was expected. And it fits the actual values on live.
With 1 epic divines trait I should get,
50% + 17% 20% = 87%
Calculation:
7802 x 1.87 = 14589.74
Since ESO lowers down decimals 14589 damage was expected. And it fits the actual values on live.
I also tested 1xInfused + 6xDivines:
Tooltip says 16% for this combination although it should give 17%.
Calculation:
7405 x 1.87 = 13847.35
Since ESO lowers down decimals 13847 damage was expected. And it fits the actual values on live.