Harry, Hermione and Ron possess a reserve of polyjuice potion when they go in search of Horcruxes.
It takes months and they use it three times:
- to go to the Ministry of Magic,
- to go to Godric's Hollow,
- to go to Gringotts.
Would this mean the potion always keeps its properties/potential as long as you haven't added the hair of the person you're turning into.