Your ears should tell you what report to give them. Not your S meter. If it means anything readability could be 59 with no S meter reading at all if they are will above the noise and perfectly readable.
Such nonsense coupling signal reports to an S meter that's different every radio, every coax and every antenna. Meaningless.
The signal report is R
eadability and S
trength and T
one if you wish. How can one hear the strength of a signal if this is clearly only a measurement of the field strength? For me it is interesting to see how strong my signal is being received. I know it is not a perfect measurement but a good indication anyway. It does not hurt to read the S-meter.
While it doesn't hurt, it also doesn't help. It literally doesn't mean a thing to a guy 5000 miles away while a true rendition of (R)eadability and (T)one does.
I can get an S9 signal and my neighbor can see that same signal at the same time on a different antenna, coax and rig as either S4 or S9+20. If the guy at the other end doesn't know this, none of it means a thing because the two of us are not calibrated against any kind of standard.
What brand is your radio? Does S9 = a 50 microvolt signal? Did you have your preamp on? Was it on +10 or +20? Was your attenuator on? Is it -6 or -10? Is your antenna a broomstick in your basement or is it a monobander at 100 feet? Which way was your beam pointed? Where are the nulls on your wire antenna? Was that long path or short path? Is your noise level S9+5?
Your S meter is just an insignificant instantaneous pointer for YOU to tell the difference of things. It means absolutely nothing to the guy on the other end because there's no way for him to make sense of it or to compare it to anything purely because of all the variables the guy on the other end cannot know.
Which why we send 59 instead of 599. The S part gets left out.
Readability and Tone. 59 or 22. Your S meter is worse than a liar. There's no truth because there's no reference to compare it to unless you figure out which stations have conditions exactly like yours. Which is pretty much none.
If you have to look at your S meter to determine strength, then perhaps it's time to stop looking at it and practice reality for a while. Put some tape over your S meter for a month and train your brain instead of using some meaningless crutch.
As far as sending QSL cards, if you didn't exchange the signal report, why would you lie about it on the card? It's not proof of anything. If I didn't exchange it, I'd leave it blank. It's about the same kind of information as 59 except without the lie.