Re: The Constellation's registry number
My "in-universe" explaination was that they had numbered it the same as an earlier Constellation. However, it was a different numbering system back then, and instead of adding a letter (such as ncc-1701-A), they just used the same number.
I wholeheartedly agree. Especially since according to the Matt Jefferies production sketch with the 17th cruiser design the "A"ppendix was originally considered for a modification or upgrade, then, but not necessarily for ships named to honor the accomplishments of a previous one.
"The first duty of every Starfleet officer is to the truth" Jean-Luc Picard
"We can't solve problems by using the same kind of thinking we used when we created them." Albert Einstein