Seed vigour drops with age even under perfect storage, and a two year old pack germinates slower and grows a weaker seedling than one from the last harvest. Potency is not affected once the plant is established, but a slow start on a short autoflower run costs yield. Breeder harvest years are shown on the product pages at https://potentthcseeds.com for most THC seeds, which is something I now check before anything else. If the shop cannot tell you when the seeds were produced, that is an answer in itself.
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