Lachenal "own Brand" Numbering

[catswhiskers]

I've been following with interest the discussions about dating Lachenals by their serial numbers. My question is whether the sequence of serial numbers applied to instruments made for various retailers' "own brand" models, was the same as that used for those bearing Lachenal's own badge.

 

I'm currently attempting to restore a very battered old Lachenal 20 key anglo (wish me luck with that!) made for Metzler & Co, serial number 90480. Using current accepted wisdom I understand this would place it somewhere around 1885.

 

Can anybody tell me if this is correct, or would a different numbering system have been used for the "own brands"?

 

Thanks in advance for your help. John