Switserland 1878-1881 - Fiber Paper?

Hi, I got these two Swiss stamps from the period 1862-1878. It's an (1881?) orange 20 and a (1878?) grey 40. I understood the paper type is important: it can be 'white' or 'fiber'. I want to verify/understand what the situation is here. In my head, the orange 20 is fiber paper, and the grey 40 is white. Correct?
On the general state of the stamps: obviously poor. I do note there is still presence of perforated paper for the grey 40. Is this of any relevance?
Finally, stampworld suggests these stamps are cancelled much more valuable than unused. Why?

The 20c is granite paper with red & blue threads(1878).These were all In-valid for use after oct. 1883,so used stamps are rarer.to bad they are in bad condition..
The cancels seemed forged.Before their issued dates...

They are both on white paper, the 30f has just been damaged by paper acidity to tone it darker. The other paper for these is granite paper and has colored threads embedded. Here is an example image (not mine) that shows the difference:

if you expand the first picture posted (back of the 20cm stamp) you'll see threads that indicate granite paper.

Thanks; granite it is for the 20f. Which leaves us with the cancel: I read 21VII73. However as you say, based on the history of this stamp any cancel is must have been stamped between OCT 1881 and OCT 1883. If you'd like to forge a cancel to e.g. increase value, why would you use a date that is not logical? That doesn't make sense to me. What if the stamp was wrongly set to 73 instead of 83?

I think Billsey, nicely, illustrates what perf12 wrote. The blackish fibres are unlikely to be a sign of granite paper. Maybe adhesion.

Bloemzee, I retract my assertion. I thought I'd seen a red thread on the right hand side, but was mistaken.