Hi Jay - I suppose the answer to your question "how do I know" is that I have been researching Carnival Glass for the past 20 plus years - and I have been especially interested in working on European Carnival makers for the last 15 years. I've travelled Europe, visited museums and libraries, flea markets, glassworks and so on and so on. I've got catalogues for all the main Carnival producers. I find European Carnival especially tantalizing and utterly compulsive. I love to research and I love to find out about previously unknown glass and unknown factories. Solving mysteries is challenging but exceptionally satisfying.
You asked
which book did I miss?
You missed my second book on Carnival Glass. "A Century of Carnival Glass". It covers all the European makers (except Poland - as I only discovered that about 6 months ago), plus India and South America. Plus all the Contemporary Carnival makers in the USA.
http://www.geocities.com/carni_glass_uk_2000/book2.htmlI know the pattern number because I have several Leerdam catalogues in front of me. The catalogue illustration of the cream jug in this pattern is illustrated in "Century".
Leerdam did not make a large amount of Carnival - mainly cream jugs and sugars, and they are usually very attractive pieces. The iridescence isn't always very vibrant, which is exactly what you described.
I'd love to put your "find" and your photos/etc on my website. I'll fully credit and acknowledge you, of course. Your comport (stemmed sugar) is a very pretty item - and I add my voice to the CONGRATULATIONS

. It will be very good to showcase Leerdam for a change
Thanks for your good wishes, I appreciate it a lot. Thanks too, to Lynne and Christine.