Short answer
Ladybird 2131 is not a calibre. Blancpain sells a ladies' line called Ladybird, and the line dates to 1956. The number 2131 in a listing is a seller tag for a batch or a revision. The number does not appear in the main public calibre lists, and no source ties it to a factory, a movement, or a year.
The Ladybird line
Blancpain introduced the Ladybird in 1956. Blancpain states the watch used the smallest round movement of its time. The name still labels Blancpain ladies' watches, including the Ladybird Ultraplate and Ladybird Colors. Case diameters differ by reference, so read the spec sheet for the model in front of you.
Blancpain calibre numbers use four digits or a mix of digits and letters, such as 1150, 1151, 1315, and 13R0. A calibre named Ladybird does not appear in that list.
Where 2131 comes from
Replica sellers tag batches with numbers and letters. You will see V1, V2, V3, plus version, or a year. Some sellers use a four digit code such as 2131. The tag records a change the seller made: dial print, hands, bracelet, movement, or packaging. The codes are not shared between sellers. Two listings with the same 2131 tag can hold different watches.
Checks before you pay
- Case diameter in mm, measured with calipers.
- Movement model, plus a photo of the rotor or the caseback engraving.
- Dial photos at 10x. Check the logo, the date window, and the print weight.
- Weight in grams.
- Reference number of the watch the replica copies, and the caseback text.
For a genuine Blancpain
The reference number sits on the caseback. The calibre number is engraved on the movement. Ask for both, plus service records. Blancpain and its retailers can verify a serial number.
Limits
The name Ladybird also labels a UK nickname for the Volkswagen Beetle and a children's book publisher. Neither relates to watches. If a listing sells Ladybird 2131 with no maker named, ask the seller for the brand and the reference before you treat the number as a spec.