I can think of a very good example of an answer to your question.
Our own "Governor Tim's" son is such an example. His son was a tall thin lefty with solid mechanics -- throwing 82-83 all summer (between his junior and senior year)
After a winter growth spurt and a continued solid conditioning and instruction over the winter of his senior year Tim's son was throwing a consistent 90 mph!
His collegiate stock soared and he eventually was drafted by the Detroit Tigers that June.
Bob,
"Doing nothing is still a course of action"