After a successful upgrade from Coresight to PI Vision on server level, What kind of Post validation procedures could be utilised to check for Data availability ?
A PI Vision upgrade doesn't really affect data availability since it is just a client tool. The only thing that could happen is that some permissions change and you lose read permissions to some of your tags but that is unlikely. Other things that can happen is perhaps your Kerberos configuration breaks after upgrade. But these are more of security issues. There won't be any data loss since you didn't make any change to your PI Server.
You can probably check that the upgrade went well by checking a few of the PI Vision displays that you often use to make sure that they are still displaying data as intended.
As Eugene Lee suggest, i would recommend to check existing displays. Other checks would be migrating displays from test to QA and QA to test to ensure version upgrade has not broken anything using display utility. Also review configuration using PI Admin configuration page. It should show all tick for AF, PI and PI Web API. Check XY plots, Event frame table using tags and AF attbutes.
Retrieving data ...