Yes IATA's RP1724 (General Conditions of Carriage (Passenger and Baggage)) is the boiler plate text (approved by many governments) for airlines' Conditions of Carriage. This is important mainly when two or more airlines may be included on the same ticket (interline), having consistent provisions actually helps the punter. However it is not obligatory, it is a Recommended Practice and airlines are expected to tailor their own CoC to suit their business model, the environment they work in and local law. Monarch are not an IATA member.
As an example this is what BA, a good IATA Member, says on Baggage: See:
British Airways - General Conditions of Carriage for the full text, 'cause I deleted a lot here.
(RP1724 contains about 10 paragraphs on this subject, sorry I couldn't find any copyable text but you can google it)
8. Baggage
8a) Your free baggage allowance
We will carry some of your baggage free of charge. Your free baggage allowance will be shown on your ticket, or in the case of an electronic ticket, on your itinerary and receipt and will depend on our baggage regulations applying at the time of your flight. If you are in doubt, please ask us or our authorised agents for details of your free baggage allowance and our baggage regulations.
8b) Excess baggage
You will have to pay a charge for the carriage of baggage over your free baggage allowance. Please ask us or our authorised agents for details of our excess baggage rates.
8c) Items you must not carry in baggage
You must not carry the following in your baggage (whether as checked baggage or unchecked baggage). [... deleted a lot of text here ...]
8d) Firearms [... deleted a lot of text here ...]
8e) Dangerous items you must not take with you on to the plane [... deleted a lot of text here ...]
8f) Fragile or perishable items must not be packed in baggage checked into the hold [... deleted a lot of text here ...]
8g) Our right to refuse to carry checked baggage not properly and securely packed
We will refuse to carry checked baggage if we reasonably believe that it is not properly and securely packed in suitable containers.
8h) Our right to search, screen and x-ray you and your baggage [... deleted a lot of text here ...]
8i) Checked baggage (baggage checked into the hold)
8i1) You must put your name on each item of checked baggage.
8i2) When you check in your checked baggage, we will give you a baggage identification tag for each piece.
8i3) We will carry your checked baggage, whenever possible, on the same aircraft as you, [... deleted a lot of text here ...]
8j) Unchecked baggage (baggage you carry on to the plane)
8j1) We set maximum dimensions and weights for unchecked baggage, which must also: fit under the seat in front of you, or fit in an enclosed storage compartment in the cabin of the aircraft.
8j2)If your unchecked baggage is larger than the maximum dimensions or weights; does not fit under the seat in front of you or in an enclosed storage compartment or we decide it is not safe,
you must check it in as checked baggage.
8j3) If you have an item of baggage (such as a musical instrument) larger or heavier [... deleted a lot of text here ...]
8k) Collecting and delivering baggage checked into the hold [... deleted a lot of text here ...]
8l) Animals [... deleted a lot of text here ...]
Although I am not a fan of BA, their Coc, albeit longer, are much clearer for the punters to understand.
So IMHO Monarchs Coc (at least as referenced in their / AVROs e-mail) fails on two accounts.
1. It fails to convey valid and accurate information to their customers,
2. Is so vague and confusing it risks being thrown out (i.e. not being considered a valid contract) under EC Directive 93/13/EEC on unfair terms in consumer contracts (and respective national law implementing such directive).
But, as I said, that's their problem.