A.
Yes, I can see that if the hazard labels all carried Class and Division numbers, as applicable, it will be more distinct. There is a long history of some 60 years behind all what we see today. Dangerous goods regulation (then called Restricted Articles Regulations) first published in 1956 was not a completed finished product. Over the many number of years, the regulations saw improvements through experiences gained. Labels introduced in 1956 were primitive and they grew up to what we see today. Hazard labels were differentiated not by class or division numbers but primarily by color, symbol and design, such as a red color label with an image of a flame will indicate “flammability”.

There is a history behind why Class 5 labels have Division numbers, e.g. 5.1 and 5.2 indicated on the label. In the beginning, both Class 5 labels were identically the same, e.g. yellow background with a symbol showing flame over a circle. To differentiate, Division numbers 5.1 and 5.2 were added. Later, to indicate a flammability with Div. 5.1 Oxidizers, the upper half of the label was made into red and the flame symbol was changed. Now the labels are distinctly different but the Panel did not touch the Division number indication. They left the number intact as the Panel did not find the need to change the division numbers into class numbers.
As for 6.1 and 6.2 hazard labels, they are governed by WHO (World Health Organization) and not by ICAO. However, WHO elected to follow ICAO pattern in differentiating by symbol and design, and chose to just indicate the class number at the bottom corner of the labels.

Class 4 hazard labels follow authentic ICAO pattern. By looking at the color, symbol and design, one can easily understand the hazard they represent. All Class 4 labels carry the flame symbol indicating “flammability”. Div. 4.1 carries red vertical bars symbolizing “flammability” (vertical bars are used to differentiate from Class 3 labels), Div. 4.2 has the bottom half in red color, and Div. 4.3 has a blue base color to indicate that it should avoid contact with water.

To make all hazard labels to carry division numbers, a motion must be moved by a member at the ICAO DG Panel. Since the issue is not a major item, I feel there is no member interested in making the motion, since the start in 1956, hazard labels were made to communicate the danger not by numbers but by the symbol, color and design of the labels.

As for radioactive material in Class 7, they are under IAEA (International Atomic Energy Agency) and they have their own rules. There is one notable contradiction with how degree of danger is indicated. ICAO uses PG I, PG II, PG III in descending order, while IAEA uses RRW-I, RRY-II and RRY-III in ascending order. With ICAO, PG I is most dangerous, while with IAEA, RRY-III is most dangerous. As ICAO and IAEA are two different branches of the United Nation, an agreement between the two may be a difficult proposition.