The novelizations of both II AND III had a lot in them that was cut from the final films. The whole Saavik/David subplot being the biggest chunk.
Fairer to say that Vonda McIntyre did lots of extrapolation as she wrote the novelizations. There was never any scripts that had actual romance between Saavik and David, just suggestive cut-away shots, posed publicity stills, etc, in much the same way as Meyer shot the alternative version of the ST II elevator scene, to suggest (in some takes) that Saavik and Kirk
Uhura's expanded part in the breakout of McCoy and the theft of the Enterprise was the other one.(Not only did she provide covert transport to the ship, but she hacked Starfleet Communications and scrambled them up so badly that only the Excelsior even knew about the attempt for some time. THEN she made a run for the Vulcan embassy.)
Again, this wasn't scripted.