Hmm. Yes and no in general. Post-lord of the Rings we have examples of variant internal traditions too, and I believe that the notably variant
The Drowning of Anadune is a later 'Tolkien-ratified' text, for example.
No doubt Tolkien was concerned with consistency, and in my opinion that is the major ingredient -- however to be 'peppered' in measure with a purposed amount of inconsistency or ambiguity, for flavour.
Another post-Lord of the Rings internal purposed inconsistency is the history of the Elessar stone. Surely we can find [or arguably find] more examples of Tolkien trying to make things consistent, but that doesn't rule out a measure of purposed ambiguity or purposed [even seeming] inconsistency in his later years.
Glorfindel is a character living in Imladris during Bilbo's lifetime [and Bilbo's stay there]. Not exactly the same scenario as with Maglor however [not that you said it was], as to my mind his ultimate fate seems far more shrouded in mythic-historical mist...
... a good case for the poetry to describe that Maglor cast himself and the Silmaril into the Sea, while another prose text says he cast not himself but the Silmaril into the Sea. Is this the case? I don't know, but I'm not sure that Tolkien would have ruled it out in a post-lord of the Rings phase even if he was naturally, and generally speaking, concerned with consistency.
Tolkien does try to re-write the existing myths, yes, but for whatever reason he never gets very far however, and we can find enough late[er] examples of JRRT characterizing the Silmarillion as a mostly Mannish account.
In my opinion this was the solution JRRT landed on rather than re-write the older, already existing legends -- at least drastically re-write them.
Maybe depends upon what a 'few' is
I myself have never been a proponent of taking Tolkien's extant work as 'all internal' and never mind the inconsistencies because it's like some Primary World example...
... however, again, I would say that
The Drowing of Anadune is a great example of purposed inconsistency due to author variation, and I believe Tolkien was happy with this variation in a post-Lord of the Rings phase of his work.