Can We Find Out..

About the Amount of Silver Involved?

 It already says (0.900) on the page 

https://en.numista.com/catalogue/index.php?e=autriche&r=&st=147-150-149&cat=y&im1=&im2=&ru=&ie=&ca=3&no=&v=&a=&dg=&i=&b=&m=49&f=&t=&t2=&w=&mt=&u=&g=&c=&wi=&sw= 

 which is the same as other years around that time. 

The total weight, not the percentage.

These 25 € coins have two segments, the outer one has a mass of 10 g the inner one 6.5 g. Now you can do the math for the fine weight 

(a simple visit to the mint's relevant page could have told you the fine weight too btw.).

You might want to up-dude this relevant suggestion:

https://en.numista.com/forum/topic145684.html

I upvoted it but they're not going to enforce it as it has been sitting there for almost two years now!

Stuff has been sitting for 10 years in suggestion hell and then was added as a feature (there is always hope).