Query about cluster metadata file - global.sts

I have an Elasticsearch cluster with version 6.6.1. I have 14 data nodes, 3 master nodes, 3 client nodes.
When I check in the above elasticsearch nodes under data/nodes/0/_state folder I can see different version of global-x.sts.
Is it required to have the same version of global-x.sts across all the nodes in cluster?

No, that's definitely not required or even expected.

In what all cases the global-x.sts version gets updated incrementally in the ES nodes?

It's incremented every time the file is written.