On the roster of Co. B, 9th VA Cavalry, in Robert K. Krick's history of the "9th VA Cavalry" for Henry Clay Rowe is says:
Rowe, Henry Clay b. 1844 in Caroline Co. att VMI. enl 3/10/62 in Co. B. Present on every roll thru 9/30/64 final roll. Paroled at Bowling Green, 5/6/65. d. 2/22/1925 in Marshall, Texas. Other Rowe's listed on the roster of the 9th VA CAV were; Rowe, Carlton
Co. B., Rowe, George W.E., Co. E., and Rowe, James W. Co. B.

To answer your 1st question, It would seem that Henry Clay Rowe may have been away attending Virginia Military Institute (VMI) at the time of the 1860 census. A check of VMI records could confirm this.

In answer to your 2nd question, in Homer D. Musselman's book, "The Caroline Light, Parker and Stafford Light Artillery" the roster for Thornton's Company list: Rowe, Clarke: enl 11/17/63 at Bowling Green, received $50 bounty, present MR (muster rolls) #9-14. Also listed is; Rowe, John T. enl. 7/23/61 as Corp. at Bowling Green. Present MR #1-14. Paroled at Bowling Green 5/1/65.

Both "9th Virginia Cavalry" by Robert K. Kirck and "The Caroline Light, Parker and Stafford Light Artillery" by Homer D. Musselman are part of "The Virginia Regimental History Series" and although both are out of print, may be available at Amazon or other book sellers on line. Also, "History of the Ninth Virginia Cavalry" by Brig. Gen. RLT Beale (published in 1899) can be found on line by doing a search for 9th VA Cavalry. Gen. Beale started as a Capt. in the 9th and rose up the chain of command to become the commander. This is a copy of a journal discovered upon the General's death and published. I hope this gives you some information to follow up on. If I can help you further, please e-mail me at rmassey6165@yahoo.com

Dr. Robert Massey
El Mirage, Arizona Territory, CSA