VPDS193100 | Vaping Products Duty and Vaping Duty Stamps: Penalties, offences and sanctions: Lost duty stamps: Definition of 'lost'
From HM Revenue & Customs · Vaping Products Duty and Vaping Duty Stamps guidance
A duty stamp is deemed to be lost if, at the end of 12 months (which begins on the date that the stamp is purchased) the stamp has not been either:
fixed to a vaping product and activated by a scanning event
destroyed
returned to the HMRC appointed stamp issuer