How was it possible for Sailor Moon to be referenced in Codename: Sailor V? I just read Codename: Sailor V and there were many references to Sailor Moon (Usagi and the other guardians making cameos, etc.), in spite of the former being created and published first. It was especially prominent towards the end, but Usagi made an appearance pretty early on. I'm interested in knowing what the publication history of Codename: Sailor V was like. And if any edits were made, what they were and when they happened. A timeline of Sailor V and Sailor Moon might also be sufficient to answer the question, if my assumption about edits is incorrect.
Codename: Sailor V first appeared as a one-shot on August 3, 1991.
The actual manga was then written pretty much simultaneously with the Sailor Moon manga, which started only a few months later (December 28, 1991) and which was updated much more frequently.
It even ended later (July 3, 1997) than the Sailor Moon manga (February 3, 1997).
That allowed for the cameos between the series.
Sources:
Codename: Sailor V Wikipedia
Sailor Moon Wikipedia
Sailor Moon Wiki