Welcome to NeuroTalk:

We have a B12 thread here with links and explanations:
http://neurotalk.psychcentral.com/thread85103.html

Basically the subject is not that difficult. However, websites that tend to be Vegan oriented, or SELL something can have confusing language. There are sites on the Web that claim you don't have to take B12 if you are a Vegan. And that is just not true. Going into biochemical details, however, is much more complex, as the following links will illustrate.

Can you tell me what sites you got the quotes from?
Our guidelines do not allow for quoting directly from sites, without giving attribution. This is because of copyright laws.
If your statements are paraphrased, then that is okay.

I see one glaring error, about Melatonin.
This link explains what melatonin does in the skin:
http://www.ncbi.nlm.nih.gov/pubmed/18155917
And what melatonin is:
http://www.uthscsa.edu/mission/spring95/brainmel.html

Melatonin is different from melanin. Melanin is what imparts the degree of pigmentation to the skin. It is genetically determined and can increase to some extent with UV light exposure. This article explains
the process of tanning:
http://en.wikipedia.org/wiki/Sun_tanning

Melatonin is completely different. It is a hormone and we are finding today, it is present in many tissues of the body. For example it is in the pancreas and the retina of the eye. It is typically an antioxidant, and also works to maintain our Circadian rhythms, called Biorhythms.(Day/night physiology).
Melatonin in the brain is made from serotonin which is a neurotransmitter, and the cofactor used is methylcobalamin (B12).

This article explains the types of cobalamin:
http://en.wikipedia.org/wiki/Vitamin_B12

The word analogue is rather outdated.
In chemistry the word analog is this:
Chemistry: A structural derivative of a parent compound that often differs from it by a single element.

In biochemistry an analog may be physiologically active or not in living organisms. Cyanocobalamin is a synthetic form of cobalamin that is an analog (some use the term vitamer) of biologically active forms. It is not active in the body until it undergoes conversion, to active forms.
Those are listed in the Wiki article I gave you.

Methylcobalamin is a biologically active form in humans.

Most commercial products containing many vitamins in mixtures use cyanocobalamin for the B12. Technically this is not biologically active, until the body changes it to a more suitable form. This is changing but slowly in some mixtures today and a few do now use methylcobalamin.

I have not found a description of how B12 is stored in the liver.
But it is. We inherited this because of our hunter gatherer lifestyles during evolution. Because food was seasonal and not always available, storage was needed for humans to survive famines.

For your B12 to be so low:
1) you were not eating animal sourced foods OR
2) you have damaged parietal cells in the stomach that make intrinsic factor to transport the microgram amounts of B12 from food into the blood stream from foods OR
3) you take drugs that impair B12 absorption, like metformin or acid blocking drugs for the heartburn/GERD-- there are other drugs that affect B12 too, but they are less common--acid is required to break down proteins OR
4) or you have some genetic error of methylation in your body.

Please read the links I've offered here, as they explain in more detail. You may have to read them more than once over time to really get the gist of them.

Take your methylcobalamin on an empty stomach for best absorption. If you do not, you risk not absorbing it correctly.
About 1% is absorbed orally, when taken correctly.