If memory serves, sea travels are given more screen time in the Companion rules, so I bet the latter two reappear later in the BECMI sequence. But I can't say for sure. I haven't owned the Companion, Masters, or Immortal rules in a long time. I do have the Rules Cyclopedia and that will get its own entry in this series.
Also absent from the Mightiest Monsters listing will be the 2nd edition of Advanced. I don't presently have any monster books for it. I really need to get a Monstrous Manual one of these days. That always struck me as a great critter book. I wish the Wizards had kept the Monstrous format for 3e. It was much cleaner and more user-friendly, in my opinion.
Just to let everyone know, I plan on covering the MM2 for 1st edition, the Rules Cyclopedia, and the Monster Manuals for 3e and 3.5. And maybe I'll offer a final general commentary post on this little project. I dunno.
In the Fiend Folio entry Gameblog reader jer left the following comment:
So, as a companion piece to these, have you thought about doing a comparison of the low-level monsters in each of the books (3HD or less)? I'm going to have to break out my Fiend Folio and see what a group of starting adventurers would be fighting in a campaign where it's the primary monster book (as opposed to "running away from in terror", which is what these posts have been showing).
Does that interest anyone else? Sounds like even more work than the present deal, but it might yield some interesting insights.