Explorators do not get Common Lore (Adeptus Mechanicus). They do get Common Lore (Machine Cult) which is not even detailed in the Skills section of the book. Are these supposed to be the same skill, or are they a divide akin to Common Lore (Imperial Creed) and Common Lore (Ecclesiarchy)? If the latter, why don't Explorators have Common Lore (Adeptus Mechanicus)?

I had considered that Common Lore (Tech) was the equivalent to Common Lore (Imperial Creed) while Common Lore (Machine Cult or Adeptus Mechanicus... pick one and stick with it) is the equivalent to Common Lore (Ecclesiarchy).

I would think that Common Lore (Adeptus Mechanicus) and Common Lore (Machine Cult) are the same thing. The former being the proper phrasing, the later being the heathen slang.

Machine Cult is in Dark Heresy. Appears to be a holdover from the design process. Note that the Seneschal is the only other class that gets CL (Adeptus Mechanicus), so I assume it was simply a typo.

Machine Cult: A general understanding of the symbols and practices of the Mechanicus, as well as such things as formal greetings and identifying rankings.

Adeptus Mechanicus: A general understanding of the symbols and practices of the Adeptus Mechanicus, as well as its hierarchy, identifiable ranks, and the existence of the Sixteen Universal laws.