What is the difference between different release dates of Android security patches?

What is the difference between different release dates of Android security patch/patches?  

There are so many different release date for different security patches for android. As there is a vast users of android across the globe so the data of that users is most important so the developers are continuously working on the security issue and resolved that by releasing different security patch/patches.

You can check you release date of Android Security patch of you device as below:-

Go to Setting -> About Phone -> Scroll Down and you can see your patch details 

According to stack overflow:-

It appears there is no official policy in place for how long a specific version is supported and no official announcement when support is dropped. Looking back through the security bulletins it appears to be consistently around 3 years after initial release that security patches stop being applied so this estimate is probably the closest thing to an answer at this point.

And you can also get the details for the security patches release by the google as CVE, Reference, Type and Security and Update details from the official site of the google developer 

 source.google.com/security/bulletin.