Also, there is a clue on the first sentence on page 1 of the datasheet:
Non-inductive construction using metalized Polypropylene....
There are two ways to build a film cap that I know: wound metallzed film, and stacked metalized film.
The statement above clearly indicates a non-inductive construction, which rules out wound film construction.
So that leaves a stacked film construction. With this type of construction, a conductive epoxy is smeared at both ends, which serves both as a conductive electrode and adhesive.
If this process is not done correctly, this joint will fail gradually. Meaning the capacitance will decrease as foil layer after foil layer becomes open circuit.
Ask me how I know..... a power supply for a remote oil well data transmitter.