Hello Sperati, welcome !

Sometimes contries at different times put the engraver and/or designer's names on the bottom of their stamps, sometimes the name(s) are in the design of the stamp(s), sometimes just the agency that the people work for (bureau of Engraving, etc)
I believe there is a site about Slania and probably books.
Better to ask general questions out on the regular forum(s) as not everyone looks in here to say hello all of the time.
And those that do look (like me at times) do not know everything. No one does really. That is why it is good to ask questions, which is contributing in a big way actually.