If all other settings are equal, seems to me Simmy ignores relief pitchers A or B designation. I haven't kept detail records (I will when new season starts) but I think as often as not it (she) is as likely to select a LR B as a LR A (or SU) . I've noticed this because I often move a RP that had a high PC from A to B for the next game. Invariably he will be 1st out anyway. Does anyone else notice this or am I hallucinating?

I have definitely noticed the opposite myself.  It seems to me like the simulation will pick the LR A over a LR B given a situation that calls for a long reliever.  However, there are other things to consider as well, such as your player settings for your pitchers.  What inning are they set to appear?  What is their auto rest setting? How many LR A pitchers do you have set, and how many LR B pitchers?  If you have only 2 LR pitchers (1 A and 1 B) and they are both set to appear at the same inning, then the LR A pitcher should be given the 1st appearance over the LR B (so long as your LR A pitcher's stamina is not below your auto rest setting). 

This seems to hold true the vast majority of the time:

Long Relief A/B - Long relief pitchers are the first to come in when the starting pitcher is removed early (generally before the 7th) in a game that is still in doubt. These are usually relief pitchers who are capable of pitching multiple innings of relief at maximum effectiveness. Unless settings in the Edit Players Settings page dictate otherwise, the long relief A pitcher will be given first priority to enter a game when this situation arises and the score is still close. If there is a wide margin in the score your long relief B pitcher will have a better chance of appearing in the game. If a long relief pitcher must leave the game during what is still a long relief situation, first replacement priority will be given to another long relief pitcher. For reference, these are also often times spot starters for teams in case of injury.