Two times I wasn't successful in claiming faulty lamps.

First, it was a CFL globe from Philips (not very cheap) purchased in Electroworld chain store. It was in 2007(?) when switching cycle wasn't specified on CFLs yet. They seemed a bit surprised when I wanted to claim it. They asked me to wait and made a phone call (probably to their corporate lawyer) and told me: "We are sorry but we cannot accept your claim as you might run this lamp 24/7 since the purchase date which is more than 6,000 hours". (In fact, it was less than 1,000 hours.) They told me if I still wanted to claim it, I had to send it directly to Philips (on my own expenses) for the analysis. I knew the results before, so I didn't bother.

Second, it was a LED bulb from Panlux . It has worked till today but sometimes it fails to start. A couple of months it starts perfectly and then it fails to start the whole evening. The ambient temperature doesn't change significantly, but usually it helps to warm it up a little with your hand. Impossible to made a warranty clam as it is going to work in the shop. I thought of damaging it (by higher voltage/electrostatics) with hope they didn't discover but I didn't it.

With the CFL: These are the tyical excuses. Youshould have insisted they give you the complete report in writing (containing yours and their arguments and signed).
Giving any such statement in writing is something they don't want at all, so they usually replace the item to just stop you from making any further "noise".
Because by law (and when it will come to the hypothetical lawsuit), they are the one, who have to prove you realy have operated it all the time. I wonder, how they will do that...

with one of my philips master led E27 12.5W i had to contact philips for an replacement (2y and 1m after the buy), they kindly sent me an replacement lamp with their excuses.

After that, because they didn't need my lamp, i made an autopsy to my lamp, with result of bad soldering in led modules, fixed and i managed to resurrect the lamp.

After some months to this fact, i discovered some lamps were recalled for this problem.