A vintage Baume & Mercier with unsigned Landeron 48 Movement

Hi esteemed OF members,

Recently came across a vintage Baume & Mercier chronograph equipped with Landeron 48 movement. The dial and case looks fine but I am concerned about the unmarked movement. Not so sure if it is normal for them to carry unsigned and unmarked movement or it was just thrown in a donor movmement?

https://m.ebay.com/itm/Vintage-BAUME-MERCIER-Geneve-Chronograph-Watch-S-Steel-case-/202266222050