No Aspartame in diet fountain drinks?

Someone tells me that diet drinks from fountains do not have aspartame, even if their canned/bottled counterparts do.

I don’t believe it, but is it true?

It’s substantially (but not completely) true.

It sounds like it’s not true – they do contain aspartame, they just also containe saccharin because aspartame decomposes in the heat and thus adding saccharin keeps the syrup sweeter longer.

Out of curiosity, what about the diet drinks that use sucralose and/or acesulfame potassium? Are those also fortified with saccharin?