You can ask for a full accounting of his estate: . . . . .
I am curious to learn from what authority you have advised the OP that he "can ask for a full accounting" of his uncle's estate?
Since he has received distribution from the estate it seems reasonable to assume that the executrix heretofore rendered her final account as required under Section 91-7-291 of the Mississippi Code.
And that the court approved the accounting and ordered such distribution following a hearing and adjudication in settlement and approval of executrix's final account and petition for order of distribution. (Mississippi Code Section 91-7-297 "Hearing and adjudication of final account")
Perhaps you have, but other than in conjunction with a petition to remove the fiduciary for cause, I have found no proviso under Mississippi law permitting an interested party to demand an accounting from an executor or administrator.
True they are entitled to file objections to the fiduciary's final account and have them aired at the Section 91-7-297 hearing, but I fail to see how the OP has any legal recourse at this point per the probate court other than to attempt to reopen the settlement hearing and set aside the court's approval of the final account and order for distribution. (And I cannot say that that itself is a viable option. Other factors may prevent it, such as having waived his right to protest the final account and petition for distribution for failure to present them timely)
However, the OP and others equally claiming they have been wrongfully denied their full inheritance do have a civil remedy to seek retribution from the fiduciary under the principle of "tortuous interference with inheritance". *
But I don't see a layperson having the wherewithal to develop sufficient evidence to support such a cause of action. And the expense of hiring a professional might be prohibitive for the OP.
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[*]"One who by fraud, duress or other tortuous means intentionally prevents another from receiving from a third person an inheritance or gift that he [or she] would otherwise have received is subject to liability to the other for loss of the inheritance or gift.
Restatement (Second) of Torts § 774B.