If the gelatin caps are stored in ware house for 1.5 year and they have expiry date of 3 years.then if they are used for product having expiry of two years how the gelatin caps will be used and what can be impact on the product?
Expiry/ Shelf life of the hard gelatin capsule is not 3 years but it is 5 years.
Then problem -
Hard gelatin capsules have a water content of 12%-15%. When moisture levels are below 12%, capsule brittleness becomes a problem. When moisture levels are above this range, deformation becomes apparent.
To maintain capsule integrity, empty capsules should be stored in closed containers under controlled conditions of 15°-25°C and 35%-55% RH. Capsule filling should also be conducted under controlled temperature and humidity conditions.
Provided the storage conditions are adequate and controlled and you already know that the shelf life of the drug product (i.e. capsules filled with excipients and drug substance) under certain conditions is 2 years, if you produce capsules with starting materials that are within each respective shelf life the shelf life of the drug product is, as you mention, 2 years.Of course what Ashish wrote is always valid.