I immersed several new vessels in the Mikvah, with recitation of the appropriate blessing before immersing the first vessel. Later I saw, that I had overseen that some of the vessels still had the sticker on it. Shall I immerse them again? If yes, with or without blessing?

Depends whether the label is on the inside or the outside of the vessel. If it is outside and you don't mind it being there and most people don't mind it being there then you you need not immerse them again. If it is a label that disturbs you - you must immerse and bless again.