Government Y/B/M fares most certainly have been instant UG eligible, but as others note, the UG does not apply until purchase. Because the standard practice is not purchase the ticket until close in (usually T-72 or closer in), there can't be an UG until that point. Thus, the benefit was relatively meaningless except for those who worked for agencies which permitted travelers to force earlier purchases (and where their Inspector General had not pushed back).

Now, the rules make it even less significant.