Your initial estimate of 1865 for the year of manufacture was not bad, and your estimate of 1868 probably was even better. My estimate is circa 1868-1869. [Louis Lachenal was producing about 900 to 1,000 English concertinas per year in that period.] The 1877 estimate is clearly way off the mark.
In my database for English-system Lachenals (over 2200 serial numbers and descriptions), No. 19070 (48 key, wood fretwork, glass buttons, 5-fold bellows) is the lowest numbered instrument labeled as "Lachenal & Co." Presumable the manufacture of this instrument dates to about 1874--right after six of Elizabeth Lachenal's workers acquired the company and changed the company name.
In my data, the highest numbered instrument with a "Louis Lachenal" label is No. 22717 (48 key, wood fretwork, metal buttons). When Ballinger-Saunders-Saunders-Crabb-Fisher-Charrierre acquired the firm, the inventory included a large stock of circular pan labels showing "Louis Lachenal." They continued to use these circular pan labels, in some instruments, by cutting off the "Louis Lachenal" but, in other instruments, leaving the Louis Lachenal on the label. Therefore, some instruments in the 19000-23000 range had "Lachenal and Co." on the exterior label in the right-side oval of the fretwork, but "Louis Lachenal" on the circular pan label.
Edited by Dowright, 12 May 2014 - 08:07 AM.