Hi Famlam,
Thank you very much for your queries about opening date and also about the sources of my edits. I have realized that while copying tags, I’ve unintentionally changed highway classification as well, so I got the changeset reverted back to the previous state. I will be more careful about this in my future edits.
I will also take caution to communicate it clearer when the local knowledge is coming from third party individuals within TomTom, not myself. I fully understand your skepticism on this matter.  
Regarding the opening dates, I have cited the information on Winkelsteeg hoofdinfrastructuur ...  . Please let me know if this information is not accurate, and you have other resources or ground truth citing August as the opening date.