"The teenager, who by this time was working in his local branch of Halfords, contacted solicitors but it went no further because he had lost the copies of the competition entry."
"However, 20 years later, he found them hidden in a set of family encyclopedias. He wrongly believed too much time had passed for another claim, although over the years he has sent several letters to the BBC asserting his rights over the character."
"Read more:
http://www.dailymail.co.uk/tvshowbi...il-Dalek-mastermind-Davros.html#ixzz1HFMCgbbX"
So he did look into making a claim at the time, but couldn't because he didn't have any proof. Then he foudn the 'proof' later.
It all fits with there being a competition entry which, as per usual policy at the time, wasn't returned, and a second, different, drawing and story which were done after Genesis had gone out and has now turned up (the one fly in this theory being that the 'story' is headed Master Steven Wright, age 13, which would be 1972-ish, not post 1975).