OK. I'll align 甘夏柑 too.

https://citruscentre.co.uk/products/natsudaidai-or-natsumikan-orange
https://www.oscartintori.it/en/prodotto/natsudaidai-or-daidai-mikan-or-natsumikan-or-japanese-summer-orange/
https://hosho.ees.hokudai.ac.jp/tsuyu/top/plt/citrus/citrus/nat.html

I can't find any real support for "Watson pomelo" outside of GG5. "Chinese citron" is an odd name for a Japanese fruit. Not common either. "Japanese summer orange" gets some use.
For 夏みかん (and 夏柑), I suggest "natsumikan (Citrus natsudaidai); Japanese summer orange".

@@ -19,3 +19,2 @@
-<gloss>summer orange</gloss>
-<gloss>Watson pomelo</gloss>
-<gloss>Chinese citron</gloss>
+<gloss>Japanese summer orange</gloss>
+<gloss g_type="expl">less sour variety of the natsumikan</gloss>

-- 甘夏	114873 (あまなつ	465506)
GG5: a Watson Pomelo; Citrus natsudaidai.
中辞典: a sweet (variety of) Watson pomelo.
ルミナス: sweet Chinese citron
-- 夏みかん/夏蜜柑  178674/15855
GG5: a Chinese citron; a Watson pomelo; a summer orange; Citrus natsudaidai.
中辞典: a Watson pomelo; a thick-skinned grapefruit-like fruit
ルミナス: Chinese citron
-- 甘夏柑  6274 (GG5 and 中辞典 merge with 甘夏
-- 川野夏橙  270 (not in the JEs)

Thanks to Brian for opening this one up. We have four entries for the various forms used for the Citrus natsudaidai. and they are obviously all over the place. The JEs also vary wildly. We should get one good set of glosses and use them for all the entries.
I'm proposing this as the gloss, and if it's approved I'll apply it to the other 3.
Note that we only use capital letters in plant, etc. names if they derive from a proper name. Hence "amanatsu".

@@ -17,3 +17,5 @@
-<gloss>Amanatsu (Citrus natsudaidai)</gloss>
-<gloss>Amanatsu orange</gloss>
-<gloss g_type="expl">less-sour variety of Citrus natsudaidai (Natsumikan), available from February to June</gloss>
+<misc>&uk;</misc>
+<gloss>amanatsu (Citrus natsudaidai)</gloss>
+<gloss>summer orange</gloss>
+<gloss>Watson pomelo</gloss>
+<gloss>Chinese citron</gloss>

夏みかん	178674	60.9%
甘夏	114873	39.1%

夏みかんと甘夏は何が違うの？見た目の見分け方や味の違いを解説
https://yuukiyasai.jp/blogs/blog/4
Called 甘 because it is *less sour* 
夏みかんよりも酸味が少ないことから「甘夏」と呼ばれていますが、正式名称は「川野夏橙（カワノナツダイダイ）」です。
Sweetness
味については、夏みかんの方が酸味が強く、甘夏の方が甘酸っぱい味わいので、実際に食べてみるとわかりやすいでしょう。
Availability
甘夏は夏みかんよりも酸味が抜けるのが早いため、2月〜6月ごろと少し時期が早めです。
夏みかんは、4月〜7月の初夏に出回ります。

(not "sweet", I've eaten several)

To lead with a complication, "when Japanese people say 夏みかん, they are often referring to 甘夏"
https://ja.wikipedia.org/wiki/ナツミカン
現在「夏蜜柑」と言えば、カワノナツダイダイ(amanatsu)を指す事が多い

So really, we've got 6~8 terms that are almost all the same thing...

===

See comments on 甘夏柑.  "Amanatsu" seems generally capitalized on google results. in our 八朔 entry "Hassaku" is capitalized.  I am not certain of the rationale.(was lowercase when I got here.  If that was correct, maybe Hassaku should be changed)

This is a common orange in grocery stores right now (and for the last two months or so, as the hassaku are disappearing), with these specific kanji (vs. other forms).  It seems odd to have a [food] tag, and be unable to use it on fruits and vegetables.  I'm not sure what the motivation is there.

I don't think the [expl] is so necessary regardless. But "Chinese citron" is only slightly more meaningful than "watson pomelo".  This isn't really adding information.  Possibly of interest is that we will have 6 terms all identified as "Citrus natsudaidai", so it might be worth noting that the　甘い half of the terms are less-sour than the non-甘い half., and that they are available in different seasons. But as I noted in the opening, that's probably not entirely true colloquially. (I say less-sour, and not "sweet", because I've eaten them. I definitely found the name to be misleading, but now I see it is the 甘い version of something that is *truly* sour).

@@ -17,2 +17,3 @@
-<gloss>amanatsu (Citrus natsudaidai)</gloss>
-<gloss g_type="expl">sweet form of Chinese citron</gloss>
+<gloss>Amanatsu (Citrus natsudaidai)</gloss>
+<gloss>Amanatsu orange</gloss>
+<gloss g_type="expl">less-sour variety of Citrus natsudaidai (Natsumikan), available from February to June</gloss>