Dates in Japanese Era Names in Unicode Standard

Dear all,

Nice to e-meet you.

I'm looking at the latest Unicode Standard [1] listing the dates for
Japanese Era Names in Table 22-8.
What I noticed is the begin and end dates for each era.
They seem to have one day difference with the dates that are recognized
publicly in Japan.
For example, the current Heisei actually started January 8th, 1989, after
Showa ended on 7th, 1989.

However, the Unicode Standard says in Table 22-8:
U+337B square era name heisei 1989-01-07 to present day
U+337C square era name syouwa 1926-12-24 to 1989-01-06

Looking at Wikipedia in Japanese [2] and English [3], you can see exact
dates for Syouwa end and Heisei start.
Could there be certain intentions to leave some difference in this
description and official dates?
Is the date counted according to GMT, instead of local date/time for some
reason?

REFERENCE

[1] http://www.unicode.org/versions/Unicode9.0.0/UnicodeStandard-9.0.pdf

[2] https://ja.wikipedia.org/wiki/%E5%B9%B3%E6%88%90
>
1989年（昭和64年）1月7日に昭和天皇が崩御して、皇太子明仁親王が即位した（今上天皇）。これを受け、元号法に基づき1989年（昭和64年）1月7日に元号法に基づき改元の政令がだされ、「平成元年1月8日」と改元がなされた。

[3] https://en.wikipedia.org/wiki/Heisei_period
> Thus, 1989 corresponds to Shōwa 64 until 7 January and Heisei 1 ... since
8 January.
> On 7 January 1989, at 07:55 JST, the Grand Steward of Japan's Imperial
Household Agency, Shōichi Fujimori, announced Emperor Hirohito's death,...
> The Heisei era went into effect immediately upon the day after Emperor
Akihito's succession to the throne on 7 January 1989.
Received on Wed Sep 28 2016 - 23:24:54 CDT