Release dates of Testcomplete patches are not available

Why do you need the release dates of the various versions?  Doesn't seem like a necessary requirement for any testing project.  

Its a requirment when it comes to postmortem bugs.

Let me give you a simple example.

From last few month there were testcases that were failing but there were other that have priority and we were busy fixing them.Now when we have started investigation and looking at automation code and app code there isn't any change that lead to testcase failure .

Now we are trying to figure out what could be the possible reason.Oe of the possible cnadiadte is may be Testcomplete upgrade.

I know dates are available  but it would be more helpful ,if they are also listed on version history page.

The release dates of TestComplete aren't going to help you in that post-mortem.  The reason being is that TestComplete is not SaaS.  So, the only way TestComplete version would change in your environments is if someone actually downloaded and installed and upgrade to TestComplete. So, even if the TestComplete release of 14 was in Early February 2019 (which it was), this does not mean, necessarily, that is what you're running right now.  Someone would have to upgrade the machine.  A better post-mortem research on these lines for your situation would be to track down when TestComplete was upgraded in your environments and use that to nail down whether or not the version change is what is doing it.