To begin with, it is highly, highly doubtful that the documents in question were the originals, nor is it likely that they were the only copies.
Now, if the originals have also been shredded, that would be something. But there is no evidence that occurred.
More interesting is the degree of cooperation between the WH and AmeriCorps on this matter, which is made quite clear by the exchange. That's where the fire is ... don't focus on non-issues.
One is not allowed to destroy documents that the destroyer has reason to believe will be required in an investigation, particularly if the destroyer (or the one who directs destruction) is an attorney.
There was an in-house counsel for Arthur Andersen & Co., the defunct accounting firm, who was criminally charged for urging destruction of documents before they were subpoenaed.
Here this was a known controversial situation. I think that the replacement inspector general is culpable if the facts are as represented.