i wonder how many people took a dump in those bars!
Doubt it,snap one in half and it should be a sandy green colour not brown/black. Proper is only black on the outside because of oxidation,if you get a big enough chunk 'off the block' and it's black inside when you snap it and it needs to be 'worked' at room temperature to get it soft and squidgy than it's low quality and not really proper gold seal despite the stamp on it (nothing more than a stamp through a sheet of 'gold leaf').
That's the same proper I used to get back in the day,it has a green tinge to it and you should be able to hold one of those bars up at one end and it'll start to bend under it's own weight cos it's so soft.
I got some of that black stuff last year from some lads that managed to smuggle a ton into Bradford,needless to say it was quite hard until you'd played with it for a few minutes and it smelled like diesel.