Since Jerry brought up consecutive serial numbers, here is the only pair of consecutively serial numbered watches I ever owned, but they are doozies: E. Howard & Co. SNs 132 and 133. Both are 17 jewel First Run E. Howard & Co. Model 1858 ("Series I") movements. Notice the differences in balance wheel spars, plate cuts, engraving styles, and dial signatures, which together reveal the rapidly evolving nature of Howard's earliest products. Movement SN 132 is in a Baldwin reversible case with matching SN. Movement SN 133 is in a gorgeous Palmers & Batchelder 18K hunting case. It was painful to let these watches go, but they both now belong to good friends.Interest and desirability of consecutive serial numbers varies among collectors, and my own interest focuses on how it demonstrates consistency or variability in watch production. However, whereas most of the time we think about consecutive movement serial numbers my research on case makers makes consecutive cases of interest too. I just bought the watch on the right in this photo and previously found the one on the left. Both have 10-size Waltham Colonial-A movements cased by H.W. Matalene around 1921.
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The cases - numbers 7203 & 7204 - are essentially identical. Over the course of 100 years #7204 has had a bow replacement and both may have gotten new crowns, but otherwise they help demonstrate the short-term consistency of his production. Another observed example of the same case is numbered 7200 and I do not know how many others may have been made in this presumed production run. About a dozen cases earlier is another example in the same style, but for Waltham's 14-size Colonial-A.