It's not sloppy writing. I should have probably been more clear earlier by what I was trying to say.
Yes, Future Ted calls Marshall "Uncle Marshall" often in the series when describing events in whatever story he's telling. Ditto Barney and Lily and Robin.
Just because Future Ted has called Robin, Lily, Barney and Marshall by their names with the preceding "Aunt/Uncle" most of the time, it doesn't necessarily mean he's going to call them that every single time
he's referenced them in his story.
This is like the tiniest needle in a haystack kind of thing to fixate on guys.