App stapling in sharepoint O365

Question

Hi, I have a scenario such as - I am having 50 site collections in SP O365 in which I have stamped an app over 5 out of 50 site collections using app stampling.

Installed the app to App Catalog and stample the app using deployment option from app call out.

Now I want to identify out of this 50 site collections which of the 5 site collections are using the app using CSOM code. 

 

Note - if we install the app to any site collection , we can call site.getAppInsatances method. But stampling of app to site collection will not give the instance of this app to the site.

Can anyone suggest me - approach for implementation. any help will  be appreciated.