I did not mean to make it sound as if you should be highly concerned about using new lifters with the old cam. I just wanted to state the best way to do it as to ensure no issues. An ounce of prevention is worth a pound of cure.

Its no more risk than a new cam with new lifters. And much less riskier than using questionable lifters. That nick in the one lifter, or having the other lifter fail again, could easily chew up your cam. I'm speaking from first hand experience. Not to mention if two were bad, what about the other 14?

Yes there have been concerns about "today's oils", which is why I recommended a Zinc additive for break-in and first oil change as a precaution. But, and nothing has been concretely proven that oil was the root cause for past problems. Other concerns were quality of the camshaft lobe materials, and the lifter material and surface grinding (which could be the problem you're having now). I've also heard of lifters not rotating in the bores (which again probably comes back to the surface grinding).

If your engine was built in 2004, it was after the time zinc additives had been reduced anyway. Meaning you broke it in with reduced-zinc oil. Also, over the past few years, new additives have been put into the oils to replace the zinc.