I have the software that recovers up to 6 characters from the private key
Any software that is not 100% open source and available to public to be reviewed is not trustworthy.
what i dont understand is how the private key ended up 4 characters short. that's really confusing. did they print it out and the printer messed up or ...i guess they wrote it down wrong on paper but that's kind of hard to believe. one mistake is undestandable but 4?
It can be a lot of different things, you already though of the printer issue and typos. There can also be damages to the storage medium (eg. paper) where some characters have become unreadable now.
4 characters is nothing, the paper could have been torn and half of it could be missing.