Is it "Mushroom" or "Mushrooms"?

While researching my book, I came to the realization that in the catalogs, our favorite fungi are identified as both Merry Mushrooms, with an "s" and Merry Mushroom, with no "s." Examining original packaging and product labels over the last year wasn't any help in determining the official name of the collection. What gives? Just an oversight by Sears?

It seems hard to believe that a huge, successful company like Sears could overlook this small, but important, detail of their most successful product, but here we are. For what it's worth, I chose Merry Mushrooms for my project because it was the large stylized name emblazoned across many of the catalog pages.

Both variations appear are in the catalogs, many times within the same catalog or even page! A survey of 44 Sears catalogs from 1970 to 1987 revealed that "Mushrooms" was used only in nine, "Mushroom" was in 16, and both were used in 15. The remaining four are when what is clearly our design was simply "mushroom design" or, in the case of the first appearance of the cookie jar in 1970, without "mushroom" even in the description.

In preparation for this blog, the catalog pages were re-examined and a vague idea began to shape itself. Was "Mushrooms" used for the large stylized name that announced the collection, and "Mushroom" to describe an individual item? It seems possible, and even grammatically correct, but this isn't always the case.
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The first three catalogs didn't even label them as Merry Mushrooms of any variety. The next six catalogs, from 1972 to 1975, it was only "Mushrooms." After a weird blip of a towel set in the 1975 Wish Book that wasn't even identified at Merry Mushrooms, the catalogs between Spring/Summer 1976 and Fall/Winter 1984 were a grab-bag of either both variations, or only one or the other.

Between the 1984 Wish Book and the 1987 Wish Book, the collection and products were always Merry Mushroom. Did an editor or product manager work hard to create consistency? Adding in original packaging and item labels only muddies the water. Sadly, this study fell short of the goal to determine once and for all if it's  "Mushroom" or "Mushrooms."

What do you think? Merry Mushroom or Merry Mushrooms?