A few of these books came out in 2018, after the animated series started. Looking at the FY 2018 10K, total revenue (for GNUS) was less than $1 million. Licensing and royalty revenue was less than $450,00 (slightly lower than for FY 2017, about $470K). Either the sales of the books are really low, low royalty rate, or GNUS doesn't get anything from the book sales.
Before, after you mentioned the different art work (for Llama Llama) on the book covers, I looked for information on the books. I found out the stories were from the animated series. Some reviews complained that the stories were not in rhyme. Book titles were also from episodes of the same name. Looking through 10Q's I couldn't find mention of any revenue stream generated solely due to the books.
If GNUS gets any revenue from these book sales, it isn't significant compared to total GNUS revenues of <$1 million (or licensing and royalty revenue of <$450,000) for FY2018, otherwise the 10K (or 10Qs) would have mentioned the material effect on revenues.
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