In his Economic Dynamics Harrod said that when he wrote The Trade 
Cycle: An Essay in 1936 the central idea of which was the interaction 
of J. M. Clark's accelerator with Kahn's multiplier, he did not have 
in his mind the fundamental growth equation. Perhaps the answer to 
your question on Harrod can be found in Harrods review of the General 
Theory. The reference to which is:
Harrod, R. F. (1937), "Mr Keynes and Traditional Theory", 
Econometrica, 5, pp. 74-86

Harrod found General Theory is static and his growth theory was to 
give a dynamic version of it. Since according to Harrod, "Keynes to 
the end refused to be interested in J. M. Clark's accelerator" 
perhaps Harrod thought that is what is lacking in Keynes.

Dipak Ghosh