I absolutely did not confirm your misinformation.
Zinchenko was not a fullback in 2017 and anyone claiming he was is just lying, stupid or has an awful memory. Neither was Delph - everyone knows this. Same goes for the following season.
Once Zinchenko had been established as a left back we technically had 4. Mendy, though, was not functional. Which is what you said. Zinchenko was still a makeshift so we really only had 2 natural and functional fullbacks.
It’s also 4 years. Not 2. Read the numbers.