Yes, this is all right-in case you only have 1 travelday left in account. IF not-then you could use 2-decide by yourself what is in your case best/cheapest way.

Also check if there is not another stop before Tarvisio but >0.00: via the planner of bahn.com=then click on train nr, is easiest for this

BUT: you need a RES for any place in NJ.

IF you come back home <31/8, kannste auch ab M mit 9€ im Nahv, fahren, das wurde länger dauern und ist gerade auf diese Strecke meist nicht sehr angenehm, da ständig gross überfüllt.

Je nach welcher Tag es wird-check auch mal auf bahn.de was eine SSP=superspar kostet M->S-mit wenigstens >1 st übergang in M-denn NJ sehr oft sehr spät-das geht of ab 19.90.

@mcadv Thank you for your answer.

This will be my last travel day in my 7 day pass. The stop before Tarvisio is Udine ( 23:48).

I am travelling on September 30th cant use 9 Euro ticket.

Do you know normally how delayed the night jet will be ? 

Where I check the history of previous night jet travels in this route ?

Do you have a Eurail pass or an Interrail pass? You write about a Eurail pass but the country in your profile is Germany.

@AnnaB I will be having Interrail pass and my family who are not in Europe will have Eurail pass.

This raises an interesting question to me , Can I consider Munich to Stuttgart also as an Inbound journey ?

You can travel in your country of residence on a maximum of two travel days. A travel day is 00.00-23.59 CE(S)T and you can board as many trains as you like during a travel day. If you travel on a night train you can stay on the train after midnight without using a new travel day. 

Whether you can travel from München to Stuttgart on your inbound journey depends on when the train from Venice to München crosses the German border. If the train crosses the border after midnight there is a way to get the arrival day of the night train as the inbound travel day and then you can continue to Stuttgart. 

I understand there will be only 1 travel day left to do Venice to Stuttgart, and that will be why the OP is buying a separate ticket from Venice to Tarvisio and will only use the pass from Tarvisio (after midnight). In that case, the bug in the app you mentioned will not be triggered.

I don’t think you can buy a separate ticket valid on the Nightjet without reservation from Venice to Tarvisio… because it is global price train.
So you need to buy a global price ticket (and I am not sure if they sell it for this route) and then extra the 14 euro for the reservation…. Maybe better to buy a ticket München-Stuttgart instead as Sparpreis (check prices). 

They do: