Is stripping old stain always required?

We moved into our house about a year ago, and have no idea when the deck was last coated. It doesn't look very good. That being said, the previous homeowners left the can of stain they once used on the deck.

If we were to buy the EXACT same stain again (no difference in brand or color), could we stain over the existing stain (which is looking patchy)? I'm not trying to go cheap on the project; rather, I'm trying to gain an understanding of the process (which I assume I'll be performing many times over the course of my deck ownership). I'd hate to completely strip the deck every few years if unnecessary.

The stain is an oil based semi-transparent.