Accidentally over curing a 3D print I'm relatively new to SLA 3D printing and 3D printing in general.  I got a budget SLA resin printer that I've been messing with for a few months now.
So I had a few soft prints laying around that have not been exposed to any UV light.  It was sunny out and I decided to bring them outside to harden them up a little bit under the sun.  And of course I forgot about them!  By the time I remembered, my prints got over cured to the point of being super brittle.
Question:  Let's say I properly cure a print (however that is). I'm not looking to paint it. It looks like the print could be accidentally over cured by taking it outside or sunlight shining from an open window.  Is that true?  Should I coat it with some kind of sealant if I'm done curing it?
You are correct, you can over cure a print by leaving it out in the sun. Prints can even over cure just by the ambient light in a room from the sun (though it would take a while).
One easy option to counter this krylon UV-Resistant Clear Coating which can be found at most hardware stores. I have used it but I found that it made my print a little softer this may have been because of the materials in the spray-can, or the type of resin I printed with.
You should check out the answer posted to Clear coating resin 3D prints as it provides some other options you can try as well such as using a brush on option.