Whats Going On With This 634?

I found this in a box lot. Not quite sure why the printing would be like this. Is it a double transfer? Over inking?
I appreciate everyone's insight and input.
Harry

This scan is not really clear enough to tell. It might be a double transfer, or overinking, but a sharp clear scan would be needed to even begin to give a real opinion.

Thanks Revcollector - I probably should have done this with the original post.
The stamp on the left is the one in question.

I'd hazard a guess that it is probably just normal fading and and maybe a bit of exposure too. It could have a re entry or over inked but sort of hard to see to really tell. I wish I could be of more help?

I don't think this is normal fading. It looks to me like something in the atmosphere has attacked the printing and perhaps the stamp paper although in the pic that part looks unchanged. How does it look on the reverse? Any staining or image bleed-through? I am suspicious that this stamp was improperly stored in some manner, possibly in contact with something having a volatile surface element. An old plasticizing agent?

Sorry to be so vague, but I would have to see the actual stamp to be any more specific.

This is one of those times when an actual viewing really is needed.