You may find that the following is of use to you, if you do not already have your answer to your question about Alexander Truman and Rebecca Letchworth.
If your birthdate for Alexander Truman is known to be around 1750, it appears that would be probable that Rebecca Letchworth is the daughter of Thomas Letchworth and Elizabeth Covington (widow of Nathaniel Skinner).
“... my Grand Daughter Rebecca Letchworth” is named in the Will of Margery Hollyday Covington Gantt, dated 16 January 1764.(PGCWR, Liber 1 folio 563 ---by PGCWR, I mean Prince George’s County Will Records).
Elizabeth Covington was the daughter of Margery Hollyday and her first husband Levin Covington. (died 1725, age 42, PGCWR Liber 1 folio 142 )
Elizabeth Covington married, first, Nathaniel Skinner, son of Robert Skinner and Ann Mackall. Nathaniel Skinner died about 1743 or 1752, (There is reason for such a discrepancy, as you will see hereafter.
By 1753 Elizabeth Covington (Skinner) married Thomas Letchworth.(See 1753 MD Archives, in the Probate Courts records of MD, Administrative Account, Liber 35 folio 272; See MD Archives Online, Probate Records, Colonial, Index) 1634-1777 Index 1, MSA S1393.)
By her first husband Skinner aforesaid, Elizabeth Covington had at least one daughter, Elizabeth Skinner, also named as a "Grand Daughter" in the Will of Margery Hollyday Covington Gantt. She married John Stone Hawkins. (See Margery Gantt’s Will aforesaid, see MD Archives Online, Vol. 58, pg. 358, and, preface pg. xxxv)
There is one other possible family origin for Rebecca Letchworth as Margery Hollyday Covington Gantt's grand daughter. She could be a second daughter of Elizabeth Covington and Nathaniel Skinner and married a different Letchworth than her mother’s second husband.
Margery's son Leonard Covington, who died in 1742 or 1741, married Priscilla Magruder and had a daughter named Rebecca, who was also named in Margery Hollyday Covington Gantt’s 1764 Will, as “my grand daughter Rebecca Mackall.” That Rebecca married Benjamin Mackall, so it is not this “Grand Daughter Rebecca” who married a Letchworth.
The inventory and accounts documents for the estate of Nathaniel Truman appear under the name of both Thomas Letchworth and Elizabeth Skinner Letchworth from November 1753 to May 1755. (See MD Archives Online, Probate Records, Colonial, Index) 1634-1777 Index 1, MSA S1393.)
Without examination of the documents, I would not hazard any guess for the death of Nathaniel Skinner other than between 1742 and 1752.. His name appears on 1740's, inventory and accounts documents filed in PGC. Since Nathaniel acted as administrator or executor for the estate of his brother, Robert Skinner, Jr., who died in 1736, there are other reasons than his own death for his name on Probate Court records. And, yet, Nathaniel Skinner may have been dead by 1744. Cannot say without looking at the documents. Those documents are available at the Maryland Archives and would answer your question, and any I raised here.
(There were various reasons for estates to be open for a longer period than 2 or 3 years, so an estate open for 12 or 13 years is possible.)
There is this reference that I have seen, Rebecca Truman filed, as the administrator or executor, an Inventory for the estate of Thomas Letchworth, June 27, 1778. (Reference to PGC Probate Records, Liber ST 1 folio 113. --This record would now be at the MD Archives. The record is cited in “Index to the Probate Records of PGC Maryland 1696-1900,” Prince George’s County Historical Society, 1988.)
If you already have an answer to the question to which I reply, and especially if it is different that the one I offer for your consideration, I would be gratified to hear from you, because there remains on my part to fit the Rebecca Letchworth somewhere. I am curious about Alexander Truman, as well, of whom I have nothing in my records, but would like to have for the Truman family.