According to Wikipedia, the first R-23 ammunition seen outside of Soviet allied countries was from a crate that was accidentally shipped to Syria with crates of 23x152B. This was then captured in Lebanon by Israel in the early 1980s. This was supposedly before it was known which weapon used it.
The same article also claims that the first time the gun was seen by any Western military was in 1987. This was when French EOD cleared the wreckage of a Libyan TU-22B shot down over Chad.
To me it seems likely that it could have been known before than, that is only the first time it was publicly confirmed.
How often are the cartridges seen in collections? There can’t be many available.