What happens if one applies a real GDP growth rate to a nominal GDP value? The result can't be a GDP figure in constant prices, since that would imply applying a real GDP growth rate to constant GDP figure.
This will provide you with a GDP in constant prices of the previous year. "Real GDP" only make sense if you mention which is you basis year. It is not an absolute figure.
Indeed, it would not make sense (beside research purposes) to display a real GDP in terms of the first year in which GDP was recorded. Accumulating 50 years on inflation in your figure would produce a tremendous discrepancy between your real GDP and your nominal GDP, resulting in confusion.