I cannot find any information about this specific instance. However, here is what I think. First one is using a sort of shorthand by writing restriction(s) instead of writing “either restriction or restrictions”.
Second, if you agree, then this question is answered by the following grammar rule: When two subjects differing in number are connected by either-or, and one of them is plural, it should be placed second and the verb should agree with it. By the way, The Elements of Grammar by Margaret Shertzer is a wonderful book on grammar, and I found the above in it on page 22.
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