yes you can integrate new and old pergo IF theya re the same thickness.

If the tongue and groove formats have changed, you will need to use their router bits to manufacture the correct tongue and groove for integration together.

the individual tiles/planks MAY have the pattern numbers and dye lots on them ... barring that i would try to get in touch with the previous owners.

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There are two ways to do any job. The right way and the wrong way. Do it right everytime.

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First of all, yes you could integrate them, but they wouldn't match....Pergo original had a different finish, and most patterns have changed, so you could continue the floor at the same level, but wouldn't have the same look. The important part here is that you have Pergo Original...which carried the Triple Plus warranty...fade, stain, wear-thru, and MOISTURE! If it's a Pergo original floor, Pergo will replace it under warranty, because Original floors were covered for just such damage as long as they were installed properly. You need to contact Pergo or your local retailer to have them come to inspect it. Hope this helps