Would you usually throw something like this out right away or grow it out a little more?
I do notice that some waterlilies I had do not put up a very good first flower after being planted. Certain flowers that are suppose to be double, may not put out double flowers until the second season or after being well established, an example is 'Miss Lucy', an oriental lily. I think I have read this is also the case for some waterlilies with exceptionally double form. For certain plants grown from seed, they might not display their "true colors" until a season later, like plumerias for example. And also, the growing condition can also affect the flowers too.
I normally consider waterlilies like this compost, however there are a few trusted friends I often ship this kind of waterlily to as they know it is just an unnamed seedling from me and will grow it out and enjoy it for the summer, but let it die in the winter. These trusted friends will not share it with others who invariably try to have it identified and often put a named variety name to this inferior plant and once again the whole market is polluted with fakes. I will not add to this pollution.
With tropical waterlilies, if a semi double or double is expected, they will look much different even on the first bloom. If I expected this one to be semi to full double, I would expect to see at least 35+ petals on the first bloom or the stamens would be modified stamenodes or petaloids. The color of the petals will stay fairly constant as well, lavender and nothing more. There are superior lavender lilies on the market that are already named. The pads on this one, while yes mottled, are not anything special.
Sure it's pretty, but it doesn't stand out enough to propagate. That is the trials and tribulations of hybridizing, trying to find something different and superior.
Cheers,
Sean