Well yes, but the Borg Invasion happened AFTER the Tezwa situation.
Yes, that's what I meant. The argument you offered may have made sense at the time of the Tezwa situation in 2379, but once February 2381 came and went, the situation had changed so much that those considerations were probably rendered moot and there was no longer any good reason to hide the truth about Tezwa.
Also.... Considering the events of Prey, where the situation escalated to a point where the relationship between the Klingons and the UFP was also not doing so well, I'm not so sure that the even bigger scandal of the Tezwa situation being revealed (even 7 years after the fact) would be settled very easily. Immidiate war.... Perhaps, perhaps not. But a withdrawing from the Khitomer Accords and ending of diplomatic relations, very likely.
Which is also part of my point. The Federation has made things worse for themselves by keeping up this lie for so long. Zife and Azernal were responsible for Tezwa, and they have long since paid for their crimes. If that were all there were to it, the Klingons might be willing to accept that justice has been served. But by hiding the truth and lying to the Klingons for seven years, the Federation has committed more affronts against the Klingons that they'd have reason to be angry about. The culpability for Tezwa lies only with the Zife administration, but the culpability for the cover-up lies with the Bacco and zh'Tarash administrations. Like the saying goes, it's not the crime that gets you, it's the cover-up. Admitting a mistake is more likely to get you forgiveness than lying about it.