Sorting my collection leads to an anomaly

I sorted my collection by silver composition and for some reason it didn't include these:

1 Peso - Mexico – Numista

They're only 10% silver but does it exclude them because it's listed as “billon”?

Love these sort features btw, thanks for all the work you've done on the site!

Yes, correct. Billon apparently doesn't equal silver.  Same for the Kennedy half dollars post 1964.  

You're right, the cutoff seems to be 50% silver content. Didn't notice 40% Kennedys aren't included either. Does that mean those silver coins aren't factored into the actual silver weight of my collection totals?

If it has a bullion value at the bottom of the page it goes into the statistic.