Interesting question re credits. See here.

I doubt you would qualify for credits as you are required to file the retailer/installer invoice and they won't be in your name.

Pella warranties are not transferrable. You can check the others on-line.

thank you, Worthy.

I also looked up ANdersen and this is on their website

"Andersen Advantage
Andersen window & doors are covered by our exclusive Owner-to-Owner® limited warranty. Most other window warranties end when a home is sold, but our coverage- 20 years on glass, ten on non-glass parts- is completely transferable from each owner to the next. And, because it is not prorated, the coverage offers full benefits, year after year, owner after owner, so it can add real value when you decide to sell your home. Plus, we have one of the largest service networks in the industry, so help is always there if you need it. Visit our Warranties section for more information."

Does this mean that that long as I get the original receipt I will be covered if I by Andersen from a private seller?

I don't think you need the original receipt for Andersens!
We bought a house with Andersen windows. Some of them had started getting foggy in extreme cold (glass panes getting too close together.) I called Andersen just to see what could be done (assumed I would have to pay for it) and they had me read them the code on the glass. Turns out they were still warrantied for 9 more months (!), so they sent someone over to repair them. I did not need to show any receipt at all.

Finding windows to fit your openings is going to be a rather lucky thing.

thanks staceyneil, that is reassuring!

brickeyee- these would be for newly cut openings or new construction so probably not an exact issue with the fit althought I would want them to match my existing windows to some degree.

"these would be for newly cut openings or new construction so probably not an exact issue "

You are going to have to revise any plans you have to reflect the window sizes you find.

Depending on what paperwork you file for a permit this could be a real PITA.