The question starts out with a lot of misinformation that if they were corrected, then the rest of the question starts to make less sense to even ask.
Master Green and Blue chalk never had lead in them. Only the chalks with lead-based pigments had lead. Those would be Yellow and Red chalks. Green and Blue pigments for Masters didn't have Yellow or Red pigment.
The lead-based pigments (yellow and red) switch to non-lead was during the global conscious effort to stop using lead-based pigments in the 70's and 80's.
So, Masters Green and Masters Blue never had lead. The couple of colors that did have lead were switched out in the 70's or 80's.
With that in mind, does the question on lead in Magic Chalk (which might not even be made in Russia) even makes sense?
http://forums.azbilliards.com/showpost.php?p=3852818&postcount=8