Evamomma, that's funny to me because one of the first words my son read was Spongebob off the tv guide channel. My daughter doesn't hide her pre-reading skills, she's solidly at the pre-reading stage, but she doesn't pre-read fluently yet either. So far she's learned what she's learned from PBS kids (word world, super why, sesame street). She points out letters & numbers regularly. Sometimes she gets them all right, sometimes she's wildly inaccurate, a few times she's said whole words, one time she stunned me by making a phonics blend of two letters on the shopping cart handle (the o & s from big lots- "o. s . os")
This reminds me when my son was becoming an emerging reader my grandmother told me, "they don't forget what they've learned. They're not just pretending that they don't know either. They just put stuff on the back burner and it's still there, brewing". With kids sometimes they can, sometimes they can't, all the way up until they can, consistantly.