Dennison used a now-opaque numbering system, making it difficult to accurately date when products premiered, short of playing detective with Bogie Books arrayed before you. It seems they used a different system based on the product: seals, illuminated silhouettes, matboards, cut-outs and the like. All seem to have been on separate tracks. Given that these are matboards and that 15 and 16 were first issued in 1914, it seems logical to assume these were issued around the same time.
Mark B. Ledenbach's vintage Halloween collectibles blog.