Are you saying that column C of the 1095-A has a number, but columns A and B are blank? 

If so, wow, that is totally wrong.

Does the taxpayer know the amount of the premiums?  It might be the same amount as the Advance credit in column C.

You or the taxpayer may be able to look up the SLCSP on the website.  You can pick which year you are looking for coverage, so you should be able to hunt down the SLCSP.

https://apply.coveredca.com/lw-shopandcompare/