Switzerland And Forged Cancels

I know that earlier Swiss stamps of the seated Helvetia design were often given bogus cancels. In a recent purchase, I found a page with several stamps of this design, some cancelled, but no indication of whether they were real or forged.

Could anyone suggest a good reference, ideally on line, to use when working through these? I have attached a scan of the page just to give some idea of what I am working with. If anyone is interested I can attach further individual scans of specific stamps.

An (outdated) site has some examples of fake Sitting Helvetia cancels
http://www.pro-philatelie.info/fael...elvetia.html
(You get a warning when accessing the (German only) site).

Thank you for the link. It will be useful particularly if I can match some of the known forged cancels with the ones on this selection. I think, though, when I create a page for them, it will just have the statement that these are common with a known example if I find one. I guess, for specialists in the
Stamps of Switzerland, it must be must be a real minefield when you are looking a a rarer specimen. I will stick to looking for watermarks, papers and perforations.