I don't know how bringing in the vision on the mount and the "ye have heard it said's", but "I say unto you's" changes between those particular things where you can find very close comparisons
Using your example,
1 Kings 22:20 And the LORD said, Who shall persuade Ahab, that he may go up and fall at Ramothgilead? And one said on this manner,
and another said on that manner.
1 Kings 22:21 And there came forth a spirit, and stood before the LORD, and said, I will persuade him.
1 Kings 22:22 And the LORD said unto him, Wherewith? And he said, I will go forth, and I will be (singular) a lying spirit in the mouth of
all his prophets (many/plural) And he said, Thou shalt persuade him, and prevail also: go forth, and do so.
1 Kings 22:23 Now therefore, behold, the LORD hath put a lying spirit (singular) in the mouth of all these thy prophets (many/plural),
and the LORD hath spoken evil concerning thee.
A scenario similar to that, would be of one spirit (in many) such as in the case of antichrist shall come, and "even now are there many" antichrists (and or many deceivers) or a liar, of a lie.
A lie, or a lying Spirit, according to the father of it for example here also
2 Thes 2:9 Even him, whose coming is after the working of Satan with all power and signs and lying wonders
"Even him"(singular).... as mentioned "In them" (who are pural) which receive not a love of the truth
2 Thes 2:10 And with all deceivableness of unrighteousness "in them" that perish; because they received not the love of the truth,
that they might be saved.
2 Thes 2:11 And for this cause God shall send "them" strong delusion G4106, that they should believe a lie
Same patern, a lying spirit pertains to their mouth of many prophets
1 Kings 22:23 Now therefore, behold, the LORD hath put a lying spirit (singular) in the mouth of all these thy prophets (many/plural),
and the LORD hath spoken evil concerning thee.
The strong delusion G4106 (in 2Thes 2:10) is same word in spirit of error G4106 (in 1 John 4:9) which is in contrast to the truth 1 John 4:9, 2 Thes 2:10) which is sent (even by God) that the same should believe a lie. (2Thes 2:11) because they received not a love of the truth.
Two different spirits
1 John 4:9 We are of God: he that knoweth God heareth us; he that is not of God heareth not us. Hereby know we the spirit of truth, and the spirit of error. G4106
1 John really springboards off this one well
John 8:47 He that is of God heareth God's words: ye therefore hear them not, because ye are not of God.
If anything they confirm between them when you compare them