IT is not a defect. !!
If visible in reflective light; it is not considered a defect.
This issue is characteristic of the product. If these lines are not visible in normal lighting, you do not have a problem.
You do, however, have an installation problem.

If I can see it from a standing position...

That is a manufacturing defect. That floor would be going back. The sample you picked the wood from, had those defects, right?

If that is not a defect according to the manufacturer, they will soon be out of business. No one will be satisfied with that.

I agree.

Thanks a lot for your valuable input. In my opinion, this is an unatural effect, and definitely a manufacturing problem.

I never noticed the problem on the samples since they were small, but it became apparent once I slapped together several bigger boards. The samples however did have the relief cuts all the way through the underlayment.

I'm still at odds on wether to send it back because of the high shipping cost. At times I try to convince myself that I can live with the problem since it's not extremely noticible and the flooring over all looks pretty good, but....?

Juan send it back. The shipping may bite but if you are anything like me it would bother you every time you notice it. Making improvements on your house should make you feel good. Is this improvement going to make you feel good? It's defective material. If you could not see it on the sample because of the sample size then the company is misrepresenting it's product.

I think that it is going back. I talked to the manufacturer today, and he indicated that he would not refund the cost of shipping the product back to them He also said that they make the relief cuts so deep because when they tried making them shallower, that caused "other" problems that made the installation harder.

I'm now considering another product from Armstrong called the Valenza Engineered Kempas (hardwoodinstaller actually has a good price on it right now). I know that some people don't think very highly of Armstrong, but I looked at this product and it appears to be very well made.

My question is, this product has a 10ply underlayment, with a very thick, 5/32" wear layer (5/8" total thickness), but the underlayment does not appear to have any relief cuts (vs. too deep on the deffective product that I'm returning). Is this something to be concerned about, or any other negative things about this product?

Those relief kerfs are there to allow the boards to flex to lay over less than flat substrates. If you prep your subfloors very flat, you should not have problems with hollow spots. Also, use the best adhesive you can afford and make sure you use the proper size notched trowel. Some think they can get a little further and use less glue by using smaller notchers, And you can. But then you will have problems with hollow spots. BTW, that Valenza is a Hartco floor. I haven't laid it personally but does look good. Take your time and it will be fine.

Standing position and not in reflective light. That is the rule of Hardwood inspections for defects.
The question is:
Are these lines visible without the reflective light from a standing position?

Thanks for your input again, Gary. I'm definitely going to do my best to prep the floor for levelness myself and I'll be using Bostix Best adhesive. What is the reccomended trowel size for this type of flooring material (Hartco 10-ply)?

If this is glued down............ The adhesive used may have swelled the boards resulting in telegrahing of the "Cuts".
Years ago, I Put hartco patterns plus in my home. The lines telegraphed, as they are with your flooring, a day or two after the installation.
The water in the adhesive swelled the wood and telegraphed to the surface.
The funny thing is; I sold that home about two years later and those "lines" had all but gone..........

Here is the National Oak Flooring and National Wood Flooring Associations Statement:
Inspection should be done from a standing position
with normal lighting. Glare, particularly from large
windows, magnifies any irregularity in the floors and
should not determine acceptance.

Didn't some guy get kicked off here a couple years ago for showing a product that had a similar problem with cuts and gaps unsupported to the wearlayer.

That floor does not look good.

That guy was removed and not for any discussion on the product itself. It was his inappropriate behavour towards others that caused that. Parts of the discussion remain somewhere.

Ken,
the lines telegraphed through AFTER that city plank was installed, I was back about 3 monthes later to install some more and the lines where gone, we Used Taylor 2071 and it swelled the relief cuts.