I'm always wary of completely ditching a GG5 gloss but I think you've made a good case that it's quite wrong. I'd prefer to call it fertilizer from the beginning.

@@ -23 +23 @@
-<gloss>dried sardines(for use as fertilizer)</gloss>
+<gloss>fertilizer made from dried sardines</gloss>

Google image result #1: Halohalo online ブログ再開しました。 2019年06月10日
Specifically distinguishes between "干物" (edible dried fish) and 干鰯(肥料 fertilizer):
干したイワシと書いて干鰯（ほしか）。干物のように見えるが、肥料。鰯を肥料に使う。歴史の授業で習ったような気がする…。

Image #3's page specifically distinguishes between edible sardines and hoshika(fertilizer)
http://bosoandante.com/2017/12/01/iwashi/#i-3
さらにイワシは食べるだけでははありません。イワシは農業を行う上非常に重要な存在になっていきます。それが、イワシを乾燥させて作る「干鰯（ほしか）」という肥料。

Image #2 on twitter mentions 干鰯 as a source of Edo-era prosperity prosperity doesn't detail how.  But if you search the reference to 「干鰯の歴史と房総の繁栄」that it cites, you get the Chiba Prefectural Museum (next reference...)
https://twitter.com/chiba_chuohaku/status/1494990414771798019

干鰯の歴史と房総の繁栄 Chiba Prefectural Museum:
http://www2.chiba-muse.or.jp/www/contents/1642581002671/index.html
江戸時代、日本中がのどから手が出るほど欲しがった肥料、それは「干鰯ほしか」です。
Fertilizer, again.

Another google image:
https://totolab.jp/2021/06/19/ととナビ13-煮干しについて/
江戸時代、食用以外にも、干鰯(ほしか)という農業用肥料に活用されるほどに大量のイワシが漁獲されました。

References for the reading ほしイワシ：　(I do not recommend adding this, however)

干しイワシ(炒め用)250g-韓国産
https://www.eprice.co.jp/shopdetail/058001000019/

ドットわん 幻の干しイワシ 8g
https://www.amazon.co.jp/ドットわん-幻の干しイワシ-8g/dp/B081ZPZ2NM

Wikipedia article on 干鰯(fertilizer only):
干鰯（ほしか）とは、イワシを乾燥させて製造した有機質肥料の一種。
https://ja.wikipedia.org/wiki/干鰯

Wikipedia article on イワシ
https://ja.wikipedia.org/wiki/イワシ
食用 section on イワシ.  If you search for 干 you'll find 煮干し（にぼし）、しらす干し。
In the 食用以外 section: 鮮魚として消費地に届けるための冷凍・冷蔵技術がなかったかつては、魚油や肥料用の干鰯が主であり.

Sorry to always be difficult...

I've proposed an alternate gloss that might be satisfactory, if I can convince you that 干鰯 is basically *always* fertilizer if you encounter it in the wild...

My concern was not the omission of "fertilizer" as a historic sense of 干鰯. Instead, at least in the backwards way I use this dictionary as a study aid for kanji, my concern was that one could learn that the translation of "dried sardine" (a common Japanese food) could be ほしか, which it isn't. (I was looking for terms using the kanji 鰯, and there aren't many to choose from). 

If we set aside the kanji for a moment, which of course literally mean "dry sardine", as far as I can tell the word「ほしか」 has only one meaning, and that is "fertilizer".  This is the one and only definition listed in wikipedia, and in a few online dictionaries.  References to 干鰯 often *explicitly* contrast it with edible fish, listing it as a fertilizer only.  

I was able to survey 3 Japanese speakers this evening (granted, hardly authoritative)... One guessed a reading of 「ほしイワシ」.  One knew the reading 「ほしか」, and reported that he had learned it in a Japanese history class (he knew it was fertilizer).  I asked them if it would be possible to use 「ほしか」 to describe the 煮干「にぼし」small dried fish that one finds as a snack, and all confirmed that that would be very incorrect/not understood.

I also did a google image search before my earlier submission.  There are indeed images of standalone dried sardines, including a subtitled TV program screenshot, but if you follow the links and read the associated articles/remaining context, they are invariably discussing fertilizer (examples in "references").

干し can be prepended to a lot of things, of course.  If you search for "干しイワシ", This gets a small selection of hits on shopping websites and such (see references).  If this database is going to include "dry sardine" as a translation of 干鰯, I would suggest that it should probably also add "ほしいわし" as a reading as well, and a note that it is usually written in kana, and that the "fertilizer" sense is only "ほしか", and that other uses are usually ほしイワシ. But ultimately I can find no evidence that 干鰯 is anything other than a fertilizer, and 干しイワシ seems no more a "word" than, for example 干杏(dried apricot), which does not appear in this database even though there are plenty of search results for it.

Sorry for the lengthy treatise on such a trivial entry.  For what it's worth, this all began when I saw that カ was not an 音読み of 鰯 (it is 和語) and got suspicious. I went googling and found out more about Edo-era fishing and farming practices than I had ever intended.

@@ -21,4 +20,0 @@
-<gloss>dried sardine</gloss>
-</sense>
-<sense>
-<pos>&n;</pos>
@@ -27 +23 @@
-<gloss>fertilizer made from dried sardines</gloss>
+<gloss>dried sardines(for use as fertilizer)</gloss>

干し鰯	196	1.0%
干鰯	2445	12.4%
乾鰯	88	0.4%
乾し鰯	0	0.0%
ほしか	16940	86.1%
GG5: 	a dried sardine
Koj, Daijr/s, Wiki, etc. say fertilizer esp Edo-Meiji
Some WWW images of dried sardines

Maybe this is the way to handle it.

@@ -5,0 +6,9 @@
+</k_ele>
+<k_ele>
+<keb>干し鰯</keb>
+</k_ele>
+<k_ele>
+<keb>乾鰯</keb>
+</k_ele>
+<k_ele>
+<keb>乾し鰯</keb>
@@ -11,0 +21,4 @@
+<gloss>dried sardine</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
@@ -13 +26,2 @@
-<gloss>fertilizer made from dried sardines (fertiliser)</gloss>
+<misc>&hist;</misc>
+<gloss>fertilizer made from dried sardines</gloss>

干鰯　ほしか　かつて肥料として使われていた、イワシを干した製品のこと
https://dic.pixiv.net/a/干鰯

http://www.archives.city.amagasaki.hyogo.jp/apedia/index.php?key=干鰯#:~:text=鰯〔いわし〕から油を,肥料として供給された。

https://kotobank.jp/word/干鰯-132968

田作はほしか(干鰯)同様に田畑の肥料にしたための名で，これを豊作の予祝の意とし，あるいは，ごまめを健康の意の〈まめ〉と取ってめでたい食品とし，祝儀や正月の膳に用いた
https://kotobank.jp/word/ごまめ-836237

Could add something like (Edo period), as this technique is apparently no longer used... 

Studying the kanji "鰯", and thought "dried sardine" was possibly useful. Was imagining something like:
1322550 煮干し 1. (small crunchy) dried sardines

Obviously 干鰯 should only be used in a very limited, specific context (Edo-era farming technology...)

The last reference shows that 干鰯 is apparently the missing historical link between the two senses of "田作り", as the farmers were fertilizing their fields with dried-sardines, and also sometimes consuming them.  But I imagine this connection exceeds the responsibilities of this dictionary.
1637250 田作り 
1. small dried sardines or anchovies (gomame) cooked almost to dryness in soy sauce and sugar​
2. tilling a rice field/ person who tills a paddy field

@@ -12 +12,2 @@
-<gloss>dried sardine</gloss>
+<xref type="see" seq="1810830">魚肥</xref>
+<gloss>fertilizer made from dried sardines (fertiliser)</gloss>