English has a tendency to change hyphenated compounds into single compound words over time. For example, “today” used to be “to-day,” and “pickup truck” used to be “pick-up truck.” This process takes a generation or so to happen. As people become more and more familiar with a phrase, they tend to leave out the hyphen. (We call this sort of thing linguistic change. Linguistic change is a common source of grumbling among grammar curmudgeons.)
Today I read an article by a reporter who covers politics. He used a compound word that I would have hyphenated. IMO the spelling is on the early side:
The decadesold informal understanding between the government and the press — that the government would only go through the motions on leak investigations — was dead.
I’m not saying he’s wrong, just early. We don’t use “decades-old” very often.
You saw it here
PS—I ran into another premature compound (for the moment, we’ll ignore the false subject and “upon” where they should use “on.”):
There is a critical need to establish organizationwide data security policies and controls based upon DSG.