Yes, if there is more than one flower on the same stalk, I would expect multiple flowers to be affected it it is a virus. I'll have to ruminate some more about the expectation of the errant white needing to be through to the backs of the petals to signify a virus; the layers of cells from top to bottom(or front to back) are not homogenous, so I don't think I would dictate that viral reactions would be homogenous throughout. Notice, for example, that the spots in the same areas seem not to be affected at all. Looking back over some other pics I have of virused flowers, this seems to be a common trait. But to be a blemish as Lorn describes, he is right that it would not affect the petal backs.
Lorn's blemish experiences are good things to keep in mind when encountering abnormalities, but in this case I don't think they apply. Wouldn't the spots (also on the surface) be effected physically in the same manner as the surrounding surface?
Barring more revealing information, my inclination is to say your flower is not virused if this pic shows the only abnormality. But I still might think about removing it or moving it to a more isolated position, just in case. Why take a chance? Of course, that's me: one who might be considered (by other gardeners) ruthless with my plants. I "throw out" plants all the time. Heck, think about all those lily bulbs I have to eat.....
