Hi TC, and thanks for the info.
I also posted these marks on the eBay Forum and someone there told me that they:
"are shown as Mark 680 in Rontgen's book and cited as the Royal Porcelain Manufactory, Nymphenburg, Bavaria, Germany, circa 1890-1895. The impressed marks of the star above the shield are also shown as Mark 606 in the Rontgen book and cited as being the Royal Factory Manufacture, Nymphenburg, ca 1850-1862."which ties up nicely with what you tell me. Unfortunately, there's no overlap of the two sets of dates ~ maybe the blanks were made between 1850-1862, stored until 1890 and decorated then? As well as the shield and star, they are impressed with '50', maybe indicating 1850?
Will try one on eBay tomorrow, and see how it goes.
Thanks again for your help ~ very much appreciated as always.
Cheers, John.