State laws vary regarding what is sufficient to establish legal title. You should ask a title attorney in the state where the minerals are located what is necessary. Texas accepts probate from other states and the probated will should be sufficient. Other states such as Oklahoma and New Mexico require ancillary probate or other procedures. Unfortunately, oil companies often accept unprobated wills and other documents to transfer royalties from deceased owner to heirs and do not tell the mineral owner that their title is unclear. If there is later a title dispute, then the mineral owner is left unprotected and has to go back to prove title. Or a later oil company under the same lease may question title. I have even seen an oil company block a title settlement among royalty owners on the grounds that some had not filed everything required in deed records, despite the fact that the oil company had accepted copies of unprobated wills to pay those owners. Too late to file probate so it was more expensive to then clear title. County clerk should not be relied on for legal advice.