Is 去年に grammatical?


I know the rules regarding when to use に with time expressions and when not
to. Or at least, I thought I knew the rules. But I watched an ANN news item
about Tsukiji market today, and at one point the presenter says「去年に...」. I
thought this was not possible grammatically.

Here's the video: <https://www.youtube.com/watch?v=R-smsxUWXys>

At 05:00 the presenter says これに対して去年 **に** 事業者が。。。

I thought it would have to be これに対して去年、事業者が。。。

Is there a definitive guide to which 'time words' will allow に and which will
definitely not?




I found 16 similar instances of 去年に on BCCWJ (excluding ones where に is
clearly needed, such as 去年に続いて, 去年に比べて). This is definitely not a large
number. Personally, 去年に does not sound terribly bad, and I feel even a native
speaker may occasionally say it, especially in speech. But it's still
unnatural and you should avoid it when possible. The same is true for 明日に,
昨日に, and so on.

