It seems that the data for speakers of Picard in France is not on here, only the data for Picard-speakers in Belgium. A source referenced on the Wikipedia article for the language cites ~500,000 speakers of the Picard language in France. Unless the source isn't reliable enough, I see no reason why it shouldn't be included in your population estimate. Even if the source isn't reliable, it might be helpful to at least mention the fact that while the exact number of speakers of this language in France is hard to obtain, it's fairly reasonable to assume that there must be a sizable amount in the country, especially since your map for France seems to say so and that you say the language originated in France. Thanks.
We will update the L1 speaker population figure for Picard [pcd] in France for the 20th edition of the Ethnologue.