The answer to the question Has the usage of the term [kinship term] changed over time? is very likely to be "yes" if enough time has passed.
For the particular question about "uncle" see "When is an Uncle Not an Uncle?"
Slippery Terms of Relationship and Status in Genealogical Records posted by Dale H. Cook on The Plymouth Colony Pages. For other terms in the colonial period, there are other references in my answer to the related question Inferring father/son relationships from Senior (Sr.) / Junior (Jr.) naming?
It is treacherous to assume 20th-century values for any usage of this kind. In Pink and Blue: Telling the Boys from the Girls in America, a discussion of the use of color as gender-marking in children's clothing, author Jo B. Paoletti notes on page 2:
The developmental stages within [the first seven years of life] have
been known by many names, including newborn, infant, child, toddler,
and preschooler, and the boundaries for those distinctions have
changed over time. This complicates the description of the
appropriate styles for each age; an 18-month old would be considered
an "infant" in 1885 and a "toddler" in 1935. For the sake of clarity,
these shifts will be noted in each section.
I use this as an example because Paoletti has given us specific dates from her research -- it demonstrates how much a commonly-used term like infant, whose meaning we think of as obvious, can change in meaning over a relatively short period of time. Assume there is a possibility for similar boundary and meaning changes for any kinship term (or age-related term) unless you have evidence to the contrary.
Note also the usage of "uncle" and "aunt" in the Southern USA as courtesy titles to address any friend of the family old enough to be a generation older than the speaker. Even terms which seem to imply a family relationship may be used for people whose relationship, according to our modern genealogy software, is associational.
Re-reading the original question, I would say that you have neglected an essential step in the analysis of your source.
Your quote is taken from a DAR Lineage book. I am not familiar with the DAR lineage books, but they are a compiled source, are they not? Are the authors for any particular entry in a lineage book known, or is the editorship known? Is anything known about the sources used when the books were compiled?
When I wrote the answer above, I was influenced by the title of the question, which was Familial Terminology in Colonial America. But you are actually a step or more removed from that. Unless you know what the primary source material is, and can examine it yourself, you don't know if the primary sources called Amos Grosvenor 'uncle' or if someone else closer in time to us has determined that relationship.
If you haven't already done so, it might be worthwhile to find out how the DAR Lineage Books came into being, so you can use the information contained within more effectively.