LTC premiums were considered a qualified medical expense in the instructions for Schedule A in 2003 (see https://www.irs.gov/pub/irs-prior/i1040sa--2003.pdf). This is important for the HSA, because validation of qualified distributions is initially based on qualified medical expenses on Schedule A.
I cannot find instructions for the 8889 on the IRS website prior to 2004 (https://www.irs.gov/pub/irs-prior/i8889--2004.pdf), but in 2004, LTC contributions were explicitly allowed, subject to age limitations (similar to today).
It appears from websites that the reason there are no instructions for 2003 is that the law was passed in 2003, to become effective on January 1, 2014 (see http://afcm.org/hsahistory.html for an example). So 2004 was the first tax year in which LTC premiums could be paid by HSA funds.
