Were gold(II) complexes synthesized for the first time in 2017? Recently in the Google news feed, I discovered this news:


  Gold stabilized in very rare oxidation state +II
  
  Missing golden link found: Divalent gold complex isolated for the
  first time in a pure form; new fundamental insight also provides
  possible explanation of the mechanism of action of cytostatic
  gold(+III) porphyrins
  
  Date: August 8, 2017
  
  Source: Johannes Gutenberg Universitaet Mainz
  
  Summary: A team of chemists has been able to isolate and analyze gold
  in the very rare oxidation state +II. This provides the missing links
  in the homologous series of the coinage metal ions copper(+II),
  silver(+II), gold(+II), and in the 'relativistic' triad of
  platinum(+II), gold(+II), and mercury(+II).


And there are loads of similar news- Here, here and here. 

Now, I started digging for more information and found out that gold(II) complexes were known previously and has been synthesized but they are unstable and prone to disproportionation.


  
  Coordination chemistry of gold(II) complexes (October 1999)
  
  The number of complexes with gold in a formal oxidation state of
  two have increased considerably and nowadays this oxidation state can
  be considered nearly as a common state in gold chemistry. This
  review covers the evolution of the knowledge of this oxidation state
  from the first dithiocarbamate derivatives $\ce{[Au2(S2CNR2)2X2]}$,
  stable only at very low temperature, to the room temperature stable
  dinuclear gold complexes $\ce{[Au2(L–L)2X2](L–L=CH2PPh2CH2, CH2PPh2S,
 C5H4PPh2-2; X=halogen}$). Although a dinuclear structure with a
  gold(II)–gold(II) bond supported by two equal bridging ligands were
  the first and most common, this review shows the present diversity as
  mononuclear, $\ce{[Au([9]aneS3)2](BF4)2}$, dinuclear with two
  different bridging ligands, $\ce{[Au2(S2CNR2)(CH2PPh2CH2)X2]}$, with a
  non-supported metal–metal bond, $\ce{[Au2(Ph2PC8H6PPh2)2Cl2](PF6)2}$,
  and polynuclear gold(II) complexes either with chains of only gold
  centers or with other metals, such as
  $\ce{[{(C6F3H2)Au(CH2PPh2CH2)2Au}2Au2(CH2PPh2CH2)2]ClO4}$ or
  $\ce{[Au2Pt(CH2PPh2S)4X2]}$
  Disproportionation of Gold(II) Complexes. A Density Functional Study of Ligand and Solvent Effects (July 13 2006)
  
  For the disproportionation of $\ce{Au(II)L3}$ complexes with neutral
  ligands, disproportionation is highly endergonic in the gas phase.
  Calculations imply that for synthesis of a monometallic $\ce{Au(II)}$
  complex, a nonpolar solvent is preferred. With the exception of
  $\ce{[Au(CO)3]^2+}$, disproportionation of $\ce{Au(II)L3}$ complexes
  to $\ce{Au(I)L}$ and $\ce{Au(III)L3}$ is exergonic in solution phase
  for the ligands investigated.
  Structural Studies of Gold(I, II, and III) Compounds with Pentafluorophenyl and Tetrahydrothiophene Ligands(February 28
  2007)
  
  A golden opportunity was seized to prepare an unbridged, dinucleur
  gold(II) compound, $\ce{[Au2(C6F5)4(tht)2]}$
  (tht=tetrahydrothiophene), without any stabilizing chelating ligands
  (see picture; Au orange, S yellow, F green, C black) and to
  crystallographically characterize the gold(I) and gold(III) complexes
  participating in this conversion. A unique ligand scrambling of the
  latter gold(III) compound occurs in solution.
  


Gold(II) complexes has been intensly studied previously. They have been trying to synthesize a stable complex but failed miserably. The stable ones are only present in low temperature and only one was found to be stable in room temperature. So, although gold(II) complexes were previously discovered and (synthesized?), why scientists at University of Mainz and those who discovered it in 2017 claims to have synthesized gold(II) complexes for the first time?
You are correct in noting that there are a number of Au (II) small molecule species synthesized prior to the report of Professor Katja Heinze in 2017.
The heart of the Au (II) claim by Professor Katja Heinze and team as stated in the article you referenced, see reference 1 given below, has to do with the a) relative stability of the mono-nuclear gold-porphyrin complexes compared to other Au (II) systems and b) that the molecule does not have a Au-Au bond.  The latter point being the more important.
Au (II) is a very stable oxidation state for molecules containing Au-Au bonds.  We synthesized and characterized a number of such species years ago, see references 2 and 3 below for two papers describing the work.
For those working in the field, the nature of the claim by Heinze et al. is understandable.  For those outside the niche field of Au (II) chemistry I can see how the distinction is less than clear.
References
https://www.sciencedaily.com/releases/2017/08/170808145949.htm
https://pubs.rsc.org/en/content/articlelanding/1985/c3/c39850001278#!divAbstract
https://pubs.rsc.org/en/content/articlelanding/1986/C3/c39860000321#!divAbstract