What is considered canon in Night Watch cycle?

Question

I asked in this question whether Zabulon really loved Alica in the Night Watch cycle. The answers there inclines

more to no, than yes.

And that Zabulon is

not capable of love.

Now I am reading the Black Palmira's Face by Vladimir Vasiliev (the novel is actually translated as Dark watch in my Czech translation) and there is the part when the narrator is stating that:

Sure, even Other is capable of falling in love deeply and no matter of how experienced make a mess like any ordinary man.

_{My personal translation, I have only a Czech copy of the book. Feel free to add official if you have one.}

That gives a new view of the original question. And it got me thinking:

1. Is Black Palmira's Face canon?
2. Vasiliev also wrote Day Watch (Дневной дозор) together with the author of the original series Sergey Lukyanenko. But it is almost certainly considered canon (as later books are referring to it). Is Day Watch less canon than other novels?
3. According to Wikipedia, Vladimir Vasilyev wrote another book from the watches universe: Time of Inversions (Время инверсий).
4. Lukyanenko wrote one short story Kid Watch, which of the scope of the novels. What about that?

So, what is considered canon?

Has, for example, Sergey Lukyanenko ever stated how much is Vasiliev canon?

Answer 1

I haven't been able to find any explicit note about "canon" from Lukyanenko himself, however, the following points stand:

In favor of everything being canon:

• all of his main 6 books and also all of the "Dozori" ("Watches") published books are listed in '"Watch" cycle' page on Lukyanenko's official web site.

• The project books by other authors are published under the heading "Sergey Lukyanenko's project 'Watches'" (Проект Сергея Лукяненко 'Дозоры'); and frequently called "franchise". This seems to indicate that they are canon of some level, having official approval from Lukyanenko.

  

• Moreover, even "Night Watch" was published under "Watches" brand:

  

In favor of the inter-author franchise books being of a "lesser" canon status (think C canon/EU in Star Wars):

• Those books were published as a separate project; and listed as a separate cycle on author's official home page.

• As far as I'm aware, nobody checks them for explicit canon compliance (ala LSG/Leeland Chee/Holocron).

  As far as I can tell, some of them were author submissions to contests and Lukyanenko's writing master-classes.

• Lukyanenko never claimed that they are official canon that I can find

Also, it's pretty obvious (and stated on author's web site) that games and films are NOT canon.