There is no identifiable trend for btsun mo across chapters, but there are clear practical trends relating to translation contexts. For example, queen is clearly the most favored usage, showing up time and again in sentences alongside kings or other royal terminology, but this translation is shifted to "Empress" when the narrative is describing female royalty in Peking. The choice of the "wife" translation is interesting in that there are a number of other words for "wife" used throughout the text (jo mo and the more precise chung mo, for example). In the first case of btsun ma as wife, in a context describing the life of Marpa, the choice might have been made based on the importance of Marpa and the partners who acted as his wives and mudras. Wife might be used alongside the term for phyag rgya/mudra for stylistic reasons here, in order not to be redundant in saying "consort and mudra" when btsun ma clearly doesn't mean queen. The more explicit use of "consort" as a translation for btsun ma might be used in cases where it's not clear if the relationship is indeed a marriage but the male figure is a prominent persona. "Lady" is an interesting choice, probably used to describe a woman of high status in a context where there is no male counterpart to define roles. Finally, the translation of "princess" is probably a mistake. There is another place where Roerich translated btsun bu as king, so he might be (correctly) interpreting some fluidity in the titles, but it seems more like an error in this case.
The overall pattern in the Blue Annals accords with what one would expect given the definition. Though not unique to the Blue Annals, the use of "btsun" to describe the wife of a king, instead of the more royal "rgyal", is important to examine. It's possible that Gö Lotsawa is trying to steer readers away from the rgyal mo seen in names such as "rgyal mo rong", a region in East Tibet, thus making it explicit that btsun mo is always a person, whereas rgyal mo might be used in names of other entities. This seems too accommodating of translation, however, as no native readers of Tibetan were likely to need such catering. Perhaps Gö Lotsawa anticipated translation and readership beyond the Tibetan elite, but distinguishing between rgyal mo and btsun mo seems too microscopic a task to have been intentionally and carefully maintained. It's more likely that the different uses reflect deeper colonizations in regular Tibetan use, one as purely titular or referential (rgyal mo), the other entailing both of these but adding more description and specific qualities (btsun mo), thus allowing for its usage to describe other kinds of people with regal qualities.
Queen: 15
"One day the king's chief queen died…" and "We shall look for another queen." (8)
"King Ikṣvāku Virūḍhaka's beloved queen…" (9)
"The two queens…" (40)
"the three chief queens" (46)
"became the queen of chi ka'o dzung" (50)
"queen Hu lun" (58)
"queen dpal gyi nang tshul ma" (100)
"having entered the womb of a certain queen of a king in India" (136)
"became the queen of srong btsan" (219)
"queen named dpal gyi 'od zer" (241)
"the spiritual teacher of the king and queen" (595)
"In the spiritual palace of North Śambhala, He was dwelling amidst five hundred queens." (814)
"the queen rdo rje bde ma" (831)
"the 'Queen' dohā" (846, 857)
"the six queens" (936)
Empress: 1
"In the tenth month he reached the Imperial Palace (Peking, chung tu) and initiated the Emperor and the Empress" (492)
Wife: 3
"Having returned to Tibet, he settled there and took bdag med ma as his wife. It is known that besides her, he had eight other wives who could be considered as his mudras (Tantric female assistants)." (402)
"His son dbon jo 'phan and his wife dug ge ma had four sons and three daughters" and "His father said to him that he would bring a wife for him" (697)
Consort: 2
"he again made offerings to ha mu and his consort" (395)
"the great official rin chen bzang po and his consort" (823)
Lady: 1
"Three sons were born to the Venerable Lady (btsun mo) red mda' ma." (213)
Name: 3
"the scholar btsun mo can (Yoṣa) of za hor" (360, 361)
"Of the three sons born to the Lady zha lu ma ma gcig gzhon nu 'bum…" (214)
"rdo rje btsun mo" (731)
Princess
"married the Princess named rdo rje gos dkar ma" (1090)