There are a few different reasons why you may not be able to see the imported tickets in your Zendesk account:
Check if you have the view that shows all tickets in Zendesk. By default, Zendesk does not have a view for every Ticket status (i.e. "Solved")
Zendesk automatically archives older tickets. Please see more about this here
If you would like an imported items report for reference of which tickets were imported, please send us a message and we can send this to you.