I did my first close last year and based on some advice I didn't do anything special for closing the main drain or floor return. The logic was that the main drain and floor return were at the bottom of the pool therefore below the frost line. It gets cold here in Ontario, Canada. In spite of this when I opened the pool this year the skimmers and returns worked and as far as I was concerned the pool was clean and ready to swim. I didn't really notice the main drain and floor return were not working until I used the heater some time late summer and didn't feel any heat coming from the floor return.
Confirmed today when I started closing. I use the main drain to bring the water level below the returns. The main drain has no suction. We used the pool all summer and didn't experience any leaks I noticed. How can I figure out if I damaged the main drain and floor return? Should I just close the pool like last year and get it pressure tested in the spring?