As you have done more then is registerd in the Score History a sinple Excel excericise with the Count function is out. You might ask WGT if they can tell you; but i wouln't hold my breath for that one.
The only other thing i can think of is a methematical solution. There is a relation between your current avg,, number of played rounds and increase/decrease of avg. after a played round. I won't/can't be exact as the WGTavg is only given in 1/100's; but it should give you an idea.
Example; Avg. is 66.00 (Avg1) and you play a round of 30(R=60, over 18 holes). After this round the avg becomes 65.95(Avg2).
Number of Rounds played = (Avg2-R)/(Avg1-Avg2)=(65.95-60)/(66-65.95)=119.
So the 30 was the 120th Legend result.
Hope this helps.