In both examples, the "Q" stands for a collective <R>, <S>, and <T> for a TMR Mark V Speedtronic turbine control panel. If the Mark V panel is a SIMPLEX panel, it refers to <R>.
The TBQB card is an optional analog I/O card used in all the control processor(s) in a Mark V Speedtronic turbine control panel.
The QTBA card is a terminal board used on every control processor of a Mark V panel.
My what a difference a letter can make; sorry, I haven't worked on a Mark V in a couple of years and I forget some things.
T<b><i>B</b></i>QB is an analog I/O terminal board, on <R> processor. If the panel is a TMR panel, there are cables from the terminal board to <S> and <T>, also. The TBQB is not usually optional.
T<b><i>C</b></i>QB is an analog I/O card, which would be in the processors on one of the card carriers. It would be optional for most turbines, required for others.
I/O terminal boards and I/O cards are not the same. (Isn't this fun?)