I had a similar problem with an order some time ago with Warm Tone developer. The labels on mine were obviously the EXPIRY dates, and the developer like yours WAS slightly darker than usual.
I contacted the seller, who happily sent me by return, two replacement bottles of fresher developer free of charge and told me to keep the other two.
Well, I had also ordered a 5 litre canister of Ilford developer, which I use the majority of the time and this is what I used for a few years until it run out. Looking through my bottles I then rediscovered the FOUR bottles of the now very out of date bottles of WT developer. Before I got rid of them, I tried them one by one, starting with the older bottles = and they have all worked fine so far. The only difference that I can find is that they don't last as long and oxidize quicker than the Ilford developer, but that may well of happened if they had been new anyway.
So, do what I did and contact the seller for replacement, telling them that they are outdated and take it from there. DON'T let them tell you that the dates are the date of production, for as you say the labels are different to the newer ones and I believe they have sold you old stock.
Terry S