In Diplomacy, is it possible for an army to be convoyed by two countries if both write the appropriate orders?

Question

There are numerous possibilities, but this one comes to mind. Italy and Austria are allies in a "Lepanto" opening (against Turkey). In the spring of 1901, Italy moves a fleet, Naples to the Ionian Sea, and Austria moves its fleet, Trieste to Adriatic Sea.

In the fall of 1901, Italy wants to move an army, which "held" in Venice in the spring, to Tunis. Austria agrees to convoy it through the Adriatic Sea to the Italian fleet in the Ionian Sea, from thence to Tunis.

So Italy writes: "Army Venice to Tunis, via convoys in Adriatic Sea and Ionian Sea. Fleet Ionian Sea convoys Army from Austrian fleet in Adriatic Sea to Tunis."

Austria writes, "Fleet Adriatic Sea convoys Italian army in Venice to Italian fleet in Ionian Sea."

Is this a valid set of orders, and will it achieve the desired result?

Answer 1

It is possible for an army to be convoyed my multiple countries (although you should write the orders differently than you did in your example).

First, the relevant rules:

Convoying an Army Across Several Water Provinces

If Fleets occupy adjacent water provinces, an Army can be convoyed through all these water provinces on one turn, landing in a coastal province adjacent to the final Fleet in the chain.

In Diagram 20, the English Army from London goes to Tunis on a single move with help from the French player.

Italy would need to write the orders:

• A Ven to Tun
• F Ion convoys A Ven to Tun

And Austria would write the order:

• F Adr convoys A Ven to Tun

From the rules:

Writing Convoy Orders

Just as “S” indicates support, the letter “C” is used to indicate convoy. Following is an example of a convoy order: A Ank–Sev; F Bla C A Ank–Sev

The reason for this is that you can potentially issue multiple convoy orders:

An Army convoyed using alternate convoy orders reaches its destination as long as at least one convoy route remains open. Orders can be written to permit more than one route for convoying an Army from its origin to its destination. The Army isn’t prevented from moving unless all routes in the order are disrupted.

Answer 2

That idea is allowable, but the exact phrasing is slightly off.

Italian orders: Army Venice to Tunis; Fleet Ionian Sea Convoy Army Venice to Tunis;

Austrian orders: Fleet Adriatic Sea Convoy Army Venice to Tunis;

Answer 3

No, those orders are not valid. Italy's orders for their army in Venice would be
A Ven-Tun

That's it. There is no room in the syntax for specifics about how that will occur, so the "via convoys..." makes no sense.

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ETA:
The fleet orders must match the army orders, and "army from ____ sea" is not valid.