First of all say damn Uniques, why do they not level up etc,. And now they do Level Up via Item-Level and get stronger up to maximum Item-Level.

It seems that Unique Items you Loot ingame (not by vendor) can may spawn at your Character-Level
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(Normal)
The O’Maley’s Lucky Belt
Required level: 20
Bonus:
+13% Status Ailment Chance Score
+13% Dodge Chance Score
+20 to All Attributes
+12% Attacks Critical Hit Chance Score
+14% Spells Critical Hit Chance Score
+40 Magic Find

, but i found ii with Item Level 51
-Screenshot -> https://ibb.co/h1mWSwn
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(Increased)
Required level: 35

Bonus:
+20% Status Ailment Chance Score
+20% Dodge Chance Score
+20 to All Attributes
+15% Attacks Critical Hit Chance Score
+20% Spells Critical Hit Chance Score
+40 Magic Find

Here is the Screenshot for you:
https://ibb.co/h1mWSwn

I am really happy that there are some "hidden-feature" things In Game, but we need to take an eye on them to find it. That is the best Gift I got so far.
To know, that other normal looted Uniques can be on a higher Item-Level, too, now.