I would say the one to the right is the more established authentic one. Without the CE Mark.
This is the original, from Mobygames.
Further, this GameFAQs shows CGB-BYTP-EUR to be the released version in this table here. A Redditor posted his/her EUR version of Crystal, and the general consensus was that it was real. Don't take their word for it, though, they might be arm chair investigators. Still, it's highly likely it's authentic.
Here's the deal though:
I can't say for sure the other's fake. The EUR-1 could be due to
The letters "CE" are the abbreviation of French phrase "Conformité Européene" which literally means "European Conformity".
The EUR.1 is most importantly recognized as a certificate of origin in the external trade in legal sense, especially within the framework of several bi- and multilateral agreements of the Pan-European preference system (the European Union Association Agreement)
Of course, I'm not saying that makes them 100% authentic, and, to be on the safer side, I suggest you take the EUR and not the EUR-1 version.