Growth is measured by weight - GSD growth charts are available if you do a google search. Here is one such site : https://www.german-shepherd-lo re.com/german-shepherd-growth- chart.html
Height is a function of genetics and cannot be controlled. What is important is to control weight to be close to what the charts specify (these charts too are approximations as genetics vary, but they give a very good guideline) The important aspect to remember is that it is better to underfeed slightly than to overfeed as overweight is far more harmful than underweight especially for big and fast growing breeds like GSDs.Excess weight during growth causes bone problems and may even lead to deformities. At the most, the slightly underfed dog will mature a few months later but the fear that it will be stunted in growth or may not gain full height etc. is totally unfounded as the final size is determined purely by genetics, not food, unless it is nutritionally deficient. So as long as you are feeding a good quality dog food and regulate the quantity by checking that the weight is as per the charts, there is no need for any other additives. Good quality dog food will ensure that all nutritional requirements are met.
By the way, for large breeds it is wise to discontinue dog food meant for puppies by the age of 6 months and switch to adult food - but the best indicator is conformity with the growth charts to ensure the pup does not put on excessive weight.