 Interesting feature
The logic seems to be simple. The first digit in the label indicates the row

position within the new matrix/vector that is being added.  Thus the first
digit remains 1
if you go on adding single rows. The second digit is then filled up by the
lowest digit 
possible that makes the label distinct from all previous labels, and the
third so on.... 
Try adding not just single rows but matrices of more than 1 rows repeatedly,

and the pattern will be clear.
 
Supratik. 

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