I cannot find a single reference to Apple thinking about ever calling OS X 10.9 "Maverick" (singular). However, I will point out:
The location Mavericks is less than 40kms from Cupertino, and very near Half-Moon Bay, where several Apple execs (including Phil Schiller) live.
Apple takes great pride in being from California ("designed in California").
Apple ran out of "big cats" names so from OSX 10.9 onwards, they will be naming them after prominent landmark/locations in California, starting with Mavericks.
Many tech companies have used place names as codenames for products. Early Macs were codenamed Maui, Malibu, Paris, Milwaukee; Intel has used almost exclusively place names for their chips (
http://en.wikipedia.org/wiki/List_of_Intel_codenames), Microsoft has used them (Fiji, Detroit, Nashville, Memphis) and AMD too (Santa Rosa, Santa Anna, Barcelona).
Apple's codenames started becoming actual product names starting with OS X 10.0 Cheetah.
It's pretty apparent to me that "Mavericks" was always the intended name.