grammatical number - No. 1, 2, 3 is right or Nos. 1, 2, 3

I cannot decide whether to add -s after words like "No.", "Fig." etc. For example, in my paper, usually I need to express:

"Fig. 1, 2 and 3 are illustrations of xxx", "This figure shows the results of frame No. 1, 2, 3 in our video"...

As you can see, there are multiple numbers after the words like "Fig.", "No.". In my option, words like "Fig." or "No." never have plural. But someone said they have. I have confused. Which one is correct?