I raised a ticket with Google play and got this response, hope it helps someone.
Hi Satheeshwaran,
Thanks for contacting Google Play Developer Support!
Regarding your concerns, the circumstance that the version code is
absent from users' reviews/comments normally results from the fact
that single use, who left comments on your app, has multiple devices,
in all of which your app was installed. The versions of your apps
installed on the multiple devices are different; therefore, the system
is unable to distinguish which version the specific user is currently
using.
Thanks for your understanding and continued support.
We hope this helps answer your question. If we can assist you further,
please let us know.
Regards, Pepper Google Play Developer Support