I'm curious about why some airplanes have accelerate-stop distance (ASD) and accelerate-go distance (AGD) in their performance charts and some don’t include that. Does anyone know why?
It depends on the aircraft in question. This isn’t required for the certification of a light twin and is solely up to the OEM’s discretion to publish said information.
So, if we use the Diamond DA62, the POH manual says...
The certification basis is JAR-23, published on 11-Mar-1994, including Amdt. 1 with some paragraphs elected to comply from CS-23 and additional requirements as laid down in CRI A-01 and published in the Type Certificate Data Sheet. The certification basis for US registered aircraft is 14 CFR Part 23 effective February 1, 1965, including Amendment 23-1 through Amendment 23-55.
I don't have any JAR knowledge but I can comment on FAR's.
(2) Procedures and speeds for carrying out an accelerate-stop in accordance with § 23.55.
(5) The effect on accelerate-stop distance, takeoff distance, and if determined, takeoff run, of runway slope and 50 percent of the headwind component and 150 percent of the tailwind component;
This specific Diamond aircraft was approved on February 1, 1965 and would have been required to meet FAR 23 but may have been granted some waivers based on JAR-23 approval. I don't know the requirements in 1965 but similar aircraft like Cessna and Piper Manuals had inaccurate information in the same time period.
In about 1985 the FAA wanted manufactures to update deficiencies in their manuals but the mfg resisted because the laws said a change would re-instate liability. Eventually congress passed a bill in 1994 that released them from liability after 18yr from mfg date and allowed changes to manuals.
I am most familiar with how this affected Cessna. Cessna manuals had deficiencies in "un-usable fuel", "emergency procedures", and "equipment operations". Cessna had addressed some issues such has equipment operations with separate "supplements". The FAA wanted all the information available to the pilot in a single manual.
Take for example the C-172. The un-usable fuel in the POH went through several changes i.e. from 1gal in 1967 to eventually 3gal in 2007 - in certain instances, even higher. The parts for the C-172 fuel system have never changed but the FAA got stricter (FAR 23.959) about calculating it.
One of the changes the FAA forced Cessna to make is an "emergency" section plainly visible (FAR 23.1581 b(2-i)) and easy for the pilot to turn to. Now, POH manuals are required to be bound in such a way they can be revised and amended (FAR 23.1581.(f)). The Cessna manuals made this change but the Diamond manual clearly is lacking this feature.
In conclusion: Diamond likely was either given a waiver, or was allowed to slip through the cracks based on the JAR-23 approval. This does happen. In addition, for some reason the FAA did not require Diamond to update deficiencies in their manual as they have done with other manufactures, and only the FAA knows why.
What will eventually happen is Diamond will get sued and they will either update the manuals or declare bankruptcy and reform under a new legal entity. (like Marvel-Schebler/Bendix/Precision Aeromotive)