Holley 2bbl date codes ?

[johnshotrods]

On the Holley 2bbl carbs that were put on the 340 or 440-6  engines is it common for them to have date codes approximately 3 months apart ?  wouldn't they have been built or date coded closer together for each engine application ?

[johnshotrods]

These are the 3 that were on the 70 cuda i recently purchased .