From the graph it can be seen that some cameras are fitted with a lens having a higher serial number than expected. This is particularly true for roll-film models. One reason for this could be that a batch of cameras was made but not always fitted with lenses, there being a minimum economic batch size determined by the time to set-up the machines and jigs. Roll-film models are relatively few in number compared to plate models and so remained in stock, without a lens, for longer. Cameras can also be found fitted with older lenses. Old, perhaps damaged, cameras might be traded in and the lenses re-used or old lenses might be bought from a source other than the manufacturer. A few cameras exist made after 1914 fitted with Tessar lenses when Zeiss imports would not have been available.

From the early 1920s the data suggests that the numbering from Ross was sequential. The situation looks different for the period during and immediately after World War I. Possibly for this period Ross was pre-allocating numbers based on orders or customer. Certainly there is a large number of lenses in the 86000 range covering a wide range of camera numbers and few between 81000 and 86000. It would appear that the first World War did not cause a great disruption to N&G production until the middle of the war. Advertisements suggest that Sibyls were available from stock until the middle of the war and that from then until around 1919 production was much reduced. But with production even in good times being so low it is difficult to be precise. Following the war the price of models nearly doubled from their pre-war figures, there was a small increase at the start of the war and later prices were available on request which may indicate that the Sibyl was still being made but at a rapidly changing cost.

The graph shows a small horizontal line at New Ideal camera E355. Four cameras with numbers E355 - E475 are fitted with Taylor Hobson lenses from a single batch having serial numbers differing by only 14. An indication of how few TTH lenses were fitted to later model Sibyls.

Following the second World War production of Sibyls may have restarted or pre-war parts were used to assemble new cameras.¹