after upgrading mongoDB 2.2.2 to 3.0.12 using 2.2.2 ->2.4.latest ->2.6.latest ->3.0.12, the data file versions are showing up as 4 and 21 as pasted below. Is it normal behavior ? please confirm.

> db.stats().dataFileVersion
{ "major" : 4, "minor" : 21 }