Artificially enhanced OT translation?

Key differences shown in blue. Verses below are from the KJV --

For David speaketh concerning him,
I foresaw the Lord always before my face, -- for he is on my right hand, that I should not be moved: (Acts 2:25)
I have set the LORD always before me: because [he is] at my right hand, ---- I shall not be moved. (Psalm 16:8) ​

Given all the other significant differences (individual words, word order, phrase order, punctuation, capitalization, verb tense) between the OT verses and the NT quotations of them, should the [italicized] words inserted into the OT rendering necessarily be exactly the same as those found in the NT translation? Doesn't this indicate that the translators were unduly influenced by the NT text in their OT renderings? Two more examples --

But Esaias is very bold, and saith,
I was found of them that sought me not; I was made manifest unto them that asked not after me. (Romans 10:20)
I am sought of [them that] asked not [for me]; I am found of [them that] sought me not:
I said, Behold me, behold me, unto a nation [that] was not called by my name. (Isaiah 65:1) ​

For it is written in the law of Moses,
Thou shalt not muzzle the mouth of the ox that treadeth out the corn. Doth God take care for oxen? (1 Corinthians 9:9)
Thou shalt not muzzle --------- the ox when he treadeth out [the corn]. (Deuteronomy 25:4) ​

Is this too obvious an effort to harmonize? Is it overly conservative translation?