As far as the rule referring specifically to words, I believe it’s just understood that “words” could be substituted with “units” or “items”. Four or more words, numbers, etc. should use the double emphasis indicator.
For your specific situation, yes the letter of the law says four or more items should use the double emphasis indicator, however you need to ask yourself a couple questions and then make a transcriber’s discretionary decision.
What do the italicized numbers refer to?
How important is it for the braille reader to know, without a doubt, that these numbers are in italics?
What is the ability level of the reader: Elementary school; College; beginning braille reader; experienced braille reader?
For example: If the italic numbers are listings of pictures, that might be important to reader so they don’t look up those pages expecting to find info in the body of the text on a specific topic.
A less experienced reader may easily miss the fact that a specific number is in italics if the double indicator is used.
You’ll have to decide which way (using the double indicator or italicizing each number individually) will most adequately suit the reader’s needs and make the print meaning most clear.
I hope this helps.