The (1982) rulebook states:

VII. THE MOVE ORDER AND THE MECHANICS OF WRITING ORDERS
On each move each Great Power may order all its units, or some, or none of them.

A unit may be ordered to do only one thing on each move: an army may be ordered to move, hold or support; a fleet may be ordered to move, hold, support, or convoy.

An illegal order is not followed, and the unit so ordered simply stands in its place.  A mistaken order, if legal, must be followed.  An order which admits of two meanings is not followed.  A badly written order, which nevertheless can have only one meaning, must be followed.

If a fleet is ordered to one of these provinces (having two coasts) and it is possible for the fleet to move to either coast, the order must specify which coast, or the fleet does not move.

XIV MISCELLANEOUS
If a player ... fails to submit orders in a given Spring or Fall season, it is assumed that civil government in his country has collapsed.  His units hold in position, but do not support each other.  If they are dislodged, they are disbanded.  No new Units are raised for this country.

If a country in civil disorder has to remove units, because it has lost supply centers, the unit farthest from home (most distant from the nearest home supply center as computed by the shortest available route, including convoys) is removed first, the fleet before the army.  If more units are equally eligible for removal than should be removed, priority is established by the names of the space in which they are located, the earliest in alphabetical order coming off first.

Unfortunately, the capacity of human players to mangle their orders is greater than the capacity of the rulebook to resolve all ambiguity.  Therefore, these house rules are provided.

A. PHILOSOPHY

1. The philosophy of these house rules is to provide complete and unambiguous interpretation of all possible mangled orders.
2. In no instance will a player be allowed to change his/her orders once the reading of orders begins.  Any comments the player makes as to the true meaning of his/her orders are ignored.  Only the orders as written are taken into account.
3. On the other hand, while these house rules are designed to provide unambiguous interpretation, the interpretation is designed to be as merciful as unambiguity will allow.

B. DEGREES OF MANGLED ORDERS

There are four degrees of order manglement.

Un-assignable.  This is an order that can not be assigned to any of the mangling player's units (or home centers, in the case of builds).

Examples:

A Canada move Bulgaria
(In Spring 1901) A Burgundy move Paris  (doesn't have an A Burgundy)
Build A Serbia
Build A Burgundy
Build F Italy.

Ambiguous.  This is an order which "admits of two meanings", or of no meaning at all.  Such an order is always treated as illegal.

Examples:

F Norwegian Sea move North  (is that North Sea or North Atlantic Ocean?)
F Mid-Atlantic move Spain  (is that North Coast or South Coast?)
A Bohemia barf Tyrolia  (what was that directive?)
A Bulgaria move Canada  (to where?)
Build Brest  (is that Army or Fleet?)
Build D Berlin  (is that Army or Fleet?)

Badly written.  This is an order "which nevertheless can have only one meaning."  The geographical context of the unit is used to clarify the meaning.  The presence or absence of nearby units is ignored.  The meaning of such an order may be legal or illegal.

Examples; all legal, except where noted:

A Marsiellse move Gascany  (mispelled)
A Marsiellse move Pairs  (mispelled, but also illegal)
F Irish Sea move North  (only North Altantic Ocean is reachable)
F Gulf of Lyon move Spain  (only one coast is reachable)
Berlin move Baltic  (doesn't specify Army or Fleet)
A Berlin support Prussia  (doesn't specify Army or Fleet being supported)
(when Trieste contains a Fleet) A Trieste move Adriatic Sea.  (Still can admit of only one meaning)
Build Moscow  (Can only be an Army)
Build D Munich  (Can only be an Army)
Build F Moscow  (Can only be an Army)
A Warsaw move to support Galicia  (use the last directive, "support")
(during adjustments phase) A Budapest  (if the player is building, this is a build. If player is removing, this is a removal.)

Well written.  These orders are crystal clear.  The meaning of such an order may be legal or illegal.

Examples of orders well written, but illegal:

A Munich move Switzerland
F North Sea move Picardy
F Denmark convoy A Kiel to Sweden
(Vienna is occupied) Build A Vienna
(Player is required to remove) Build F Rome

C. PROCEDURE

If multiple sets of orders are turned in by the same player, only the latest set is used (especially if labeled "2nd set").  Also, mislabeled sets of orders (country missing, wrong date, etc.) are still used.

All un-assignable orders are ignored.

If multiple orders are assigned to the same unit, then the last legal order for that unit supercedes the other orders.  Note: a support or convoy order which is not utilized by any beneficiary is still considered a legal order.

If it is the adjustments phase, the player is required to remove units, and the player did not provide enough legal remove orders; then the legal orders that were provided are followed, and the remainder of the removals are accomplished via the civil disorder rules.

If it is the adjustments phase, the player is allowed to build units, and the player provided too many legal build orders; then begin with the first order and follow each one in turn, stopping after the allowed number is reached.

D. IF ALL ELSE FAILS

If there is still ambiguity, the word of a non-playing GM is final.  If there is no GM, then a vote is taken by all players, whether they have been eliminated from the game or not.  If an eliminated player has left the premises, and there is an even number of players physically present, then the player whose orders are in question does not vote.