Hi Abhishek,
In case of nodes with numbers, any node starting with 0, this 0 gets omitted in the search query.
So, if your node name is like 02013 for year, when it searches it omits 0 and searches for 2013.
In case you want to search for your node, your SQL2 query should be like below:
SELECT * FROM [nt:base] AS s WHERE ISDESCENDANTNODE(['/content/mysite/en/products/2013/05'])
See screenshot for reference. This should return you the results.
Hope this helps.
I guess for more reference on SQL2 queries, you can refer to JCR 2.0 spec.
http://www.day.com/specs/jcr/2.0/6_Query.html
Also, you might want to look at the railroad diagrams and some examples from Jackrabbit's test cases:
http://www.h2database.com/jcr/grammar.html
Hope this helps.