This is definately true.
I have recently realised that my fiancee has what I call different modes of ticklishness.
Her feet, arms, behind the knees, sides and neck are always ticklish spots. But when I tickle her enough, her whole body becomes super ticklish and places which were previously not ticklish are ticklish.
Her ears being one, I was affectionately kissing her ear and she burst out giggling in surprise, her shoulders as well seem to be another and some other spots.
As for the super ticklishness, I was able to make her giggle herself silly, just from tracing my fingers up and down and gently poking her sides through her dress.
Also one morning in bed I gently touched one of her barefeet and she pulled it away.
I did the same thing again only for her to pull her foot away again, "Oh come on I said i'm not even tickling you." I grabbed the foot with one hand and proceeded to just keep gently putting my hand on this foot, she now started laughing and trying to pull the foot away. Her feet were super ticklish to my touch! I didn't even know that was possible!
The best part is I have realised, her body is sometimes already in super ticklish mode without me tickling her first.
But yes if she isn't in the mode, I put her in to it when I tickle her.