Yes you are correct that the code does say that a "tack welder" is certified indefinately in the positions and processes in which they are qualified.
I have found it easier to still "re-certify" my tack welders every 6 months even though it is not required.  I do this only as a precaution on my part becasue I have SO many outside inspectors and engineers reviewing my certs and re-quals that I didn't want to get into an argument with them on this clause.
Is it above and beyond what is called for? yes, do I have to do it? no. But again I have people with different levels of knowledge of the code and instead of me teaching everyone about this stipulation, I decided to just go with the flow and re-certify them and document it every six months.
Now remember to "requalify" is easy.  It's just confirming and documenting that they are welding with the process and position they are qualified for, it's not an actual test.  I use welds off of the production floor to re-qual my guys and write it down and keep it in a file, not too hard, a little time consuming, the longest part is typing it up.  Note this is assuming the welds they put in are passing a visual inspection.
Good Luck

correct, I do keep a welders continuity log for my "tack" welders as well as my "regular" welders.