Is the existing laminate and the new laminate from the same dye lot/manufacturer run? We ran into a similar situation where our 1yr old laminate that was not installed correctly was glossier than the laminate they were replacing it with. They reused our existing boards on the perimeter and used new planks for the rest and there was a clear difference. They were the same floors but manufactured at different dates so the dye lot or whatever was different.

Yes, all bought at the same time, etc. We didn't have to pick and choose during the first installation. Now all boxes left are the same, but dull, no shine.

same dye lot and all.

Maybe off gassing caused discoloration if the boxes were sealed tight.

yes.

I would say the difference is merely the lack of "cleaning" of the stored boxes. Your floors have 10 years of 'wear' which means 'buffing'. As you walk across a floor, you are slowly 'buffing' the floors. And buffing means added shine/gloss level. A mechanical 'polishing' if you will.

And every time you cleaned your floor (mop, water, etc) means removal of dirt = light buffing. Personally I would install the laminate, clean it and be thankful that you had the forethought to purchase enough for your entire home.

I know this feels like a a complete loss, but it isn't. It is just a difference of sheen that life makes possible through cleaning.

If you really want to know what's up, go ahead and use some windex on a loose plank (from the box). Give it a LOT of elbow grease (I would clean it 2-3 times). The first clean = ++ windex with 30 seconds of 'sitting' and then wipe down with a CLEAN white cotton cloth. Add +++effort/rubbing/pressure on the planks. Clean it like you mean it! The second clean comes a few seconds later with a LIGHT MISTING of windex and then wipe IMMEDIATELY with a NEW cotton cloth. Add a snick of pressure. If your cloth still picks up a bit of dirt/colour, then do it a third time.

Windex has ammonia in it. It also has ALCOHOL in it which means it evaporates QUICKLY and that means it won't damage the laminate because of 'wet'. That's why you can use +++Windex on the first application and let it sit. It is also a degreaser. It also ensures there will be zero film left over (because it is made for glass...).

I would keep doing the 'cleaning' with the windex (new white cotton cloth each time) until the cloth comes up clean. Only the FIRST dose of windex = heavy misting. All the rest of the cleaning is light misting...one maybe two squirts for a single plank.

Once you have cleaned up/polished up a SINGLE plank...go ahead and compare the gloss level to your existing flooring AND to the dirty planks in the box. I'm going to guess that the single plank will sit somewhere BETWEEN the gloss level of your buffed/lived on floor and the dirty/gungy 'in the box' planks.

And that's what you are looking for. You are looking to confirm that your 'in the box' laminate planks will clean up/buff up over time. With that knowledge, you can then go ahead and install that dirty/gungy in the box stuff knowing that it will 'buff up' just like the rest of your floors.

Just give it time and a few years of cleaning. The two floors will eventually even out.

And don't forget your transition strips through doorways will also hide the slight difference in gloss level. That and the furniture will hide most of the issue.

I have the exact same problem. We did some construction in our kitchen and had to replace random boards in the middle of our floors with left overs from 10 years ago. Your answer here gives me hope that I can bring the sheen of the old boards up to the ones that have been in place for 10 years. Thank you!