I have a data point to add. About a year ago (May 2017) I ordered a #10 can of Mountain House freeze-dried chicken. I opened it not long after. I threw in several moisture absorbing packets, and one oxygen absorbing packet, and kept the can in a dark kitchen cabinet, in an air conditioned house, opening it occasionally. It is now August 2018 and I’m almost finished with the chicken.
I tested out a backpacking meal at home yesterday, using a small amount of said chicken. Tastes the same to me :-) I have a healthy immune system and rarely get sick from food, so keep that in mind. However, the chicken is still super dry… looks the same as the day I opened it. The can says to use immediately, but may still be OK for up to one week.
I also have a #10 can of MH Breakfast Skillet, opened on May 10th 2018. Haven’t added any moisture or oxygen absorbing packets to that yet. Ate a serving of that on my backpack last weekend, no problems either, and taste is fine.
As Doug said, YMMV :-)