Of course it does; the issue is not the word or even whether it was a later insertion. Christ was a firstborn as a Jewish legal term, regardless of other siblings. This is another englishism you introduce, when you imply that since Christ was a firstborn, there have to be a "secondborn".
When an American mother introduces her children she might say: "This is Josh, my first...", and even if her speech were interrupted at that point by a malfunctioninig coffee maker, we'd know that she gave birth to more than one child. But that is because nothing legal attaches to being the elder brother in America. To a Jew that would mean an obligation to God and transfer of title. When Matthew mentions "firstborn" it is to underscore that in His earthly genealogy Christ is in the line of King David. Little would he know that 2,000 years later people not familiar with the Jewish law or the working of dynasties would read stuff into it.
-A8
"When an American mother introduces her children she might say: "This is Josh, my first...", and even if her speech were interrupted at that point by a malfunctioninig coffee maker, we'd know that she gave birth to more than one child."
I like to introduce my oldest, in the presence od my wife and with a perfectly straight face, "This is John, my oldest from my first marriage" 'Course I've only been married once. :)
Whether it is an insertion isn't even the point - since Luke 2:7 also includes the phrase.
It isn't an Englishism when I looked it up in the lexicon. What is a prototype? It is the first in a line of items.
Prototokos came from two Greek Roots.
Protos- which has these meanings:
1) first in time or place
a) in any succession of things or persons
2) first in rank
a) influence, honour
b) chief
c) principal
3) first, at the first
And Tikto meaning:
1) to bring forth, bear, produce (fruit from the seed)
a) of a woman giving birth
b) of the earth bringing forth its fruits
c) metaph. to bear, bring forth
So Mary gave birth to either her:first in time or place,
in any succession of things or persons, highest ranked, her chief, principal, or most influential Son. This is Jesus in relation to Mary.