212, good spot but I too can't see what that discrete is. I don't think its worth trying to guess.
The DME is only recorded to the mile, not decimals of a mile, hence it changing in steps of 1 mile. So its a resolution issue rather than a sample rate issue.
On the VS trace, I can only guess you are right and (not having been involved in the L2 for 7 years) I can't remember how the AFCS behaves once you go below the min speed for a mode. On the L, it remains engaged. On the 225 it drops out (though the vertical modes all work down to zero kts). Not sure about the L2.