Lot number is not being saved in stock move

When I create a sale from POS or Sale module and select a product lot, and pay. After this process when I check the stock move, it does not store lot number which was selected while creating the sale.

Secondly, is this the reason why even after sale from a specific lot, in next sale lot shows the same quantity as it was before making the sale

If Lot is not connected with QTY, then how to implement FIFO or FEFO for medicine?

There is no standard module that adds lot on the sale nor POS lines.

You can see the quantities of a product by lot.

Often such picking policy does not need to be implemented in the software but it is a practice of stock management (like the order products are stored and then picked).

Remember lot in Tryton are just a tag not a constraint.