Very hard to prove that NL made the Grillo sisters an offer. Hard for NL to prove that wasn't the case either, but since they relied on the quid pro quo defence then I think she would be justified in trying to recoup from them their ill gotten gains -- I don't know if a civil action is possible in a case like this but I have an idea the standard of proof is looser for civil cases than if a criminal case were brought.
The financial assistant who was fired (now the owner of an art gallery) was supposed to go over the statements and assign each line to a certain category of expenses, so it's possible this was what he used to repay certain expenses to the company, and this seems to have been an ongoing method of keeping money moving around over the years. This may have been ok depending on what sort of incorporation CS's company has, though I imagine the revenue commissioners will be rolling up their sleeves and sharpening their pencils even as we all type..
IIRC, the drug secret/wild spending relationship was only introduced as a defence many months after the Grillo sisters were initially charged, which leads me to conclude they were clutching at straws. CS's email (motivated by personal animosity towards NL) that claimed he believed every word the Grillos spewed on the subject of NL and drugs actually hurt him financially in the end.
I suspect the guilty secret defence is only used when someone has a personal axe to grind and/or is encouraged by someone with an axe to grind, or is really desperate to get away with what they have done.