Eddy del Rio
The 26-July rally @ base mechanism (2x bases + 2x population in guerrillas) is just about the most efficient rally @ base formula for any faction in any game across the whole COIN series (I realize that might not be a great comparison). 2 bases in the Sierra Maestra (obviously easy to set up given that you start with 1 there) nets 6 guerrillas for 1 resource; this obviously increases to 8 for 1 if you set up 2 bases in Las Villas or Oriente. That's more than half of the 26-July force pool in one rally. In my plays of the game, this hyper-efficient rally mechanism, combined with the generally lower piece count in Cuba Libre compared to the other COIN series games, means that 26-July will easily have all their pieces on the board in the first couple of turns, and don't have any problems replacing mass amounts of pieces in just one Op if they ever take significant losses.
I'm curious if there's a historical design reason behind the efficiency of 26-July's rallying/recruiting? I certainly don't consider myself an expert by any stretch of the imagination, but I've done a reasonable amount of study on the period of the Castro's revolution and if anything it seemed like 26-July actually had a fairly hard time recruiting new members into the organization, at least initially. I can make a few guesses as to why the faction gets 2x rallying, but would love to hear other people's thoughts.
I think your question is addressed on page 28 of the Play Book (Design Notes), right column, paragraphs 3 (26 July Movement) and 4 (Urban Guerrillas).