If we're keeping the 創世期 entry, I think 創世期 needs to be visible here as well. iK is probably best.
I don't think the examples are needed.

@@ -21,2 +21,2 @@
-<gloss>early days (e.g. of a company)</gloss>
-<gloss>early years (e.g. of an industry)</gloss>
+<gloss>early days</gloss>
+<gloss>early years</gloss>

https://eow.alc.co.jp/search?q=創世期
創世期に
in the early days（ある時代の）

An example: a musician who supported death metal in its formative years:
デス・メタル・シーン創世期を支えた重鎮バンド OBITUARY
https://gekirock.com/news/2018/03/obituary_live_video.php

創成期	24689	52.7%
創生期	15270	32.6%
創世期	6930	14.8%


"創世期" site:twitter.com
* A社の創世期について詳しく話を聞いた ...
* #TomsRacing の創世期を支えたレーシングカーKP47 ...
* 一人目は、創世期から奈良クラブを支え、...
* 日本SF創世期にこんな書き手がいたとは

twitter googits:
創成期 ~3000
創生期 ~550 ("did you mean "創世記"?)
創世期 ~220
the book of Genesis
創世記 ~ 5,860

Note: 創世記 is used in a trendy way as just "Genesis", without appearing to refer to the Biblical text.

I didn't realize eijiro had "early days" on 創世期 as well. A search for:
site:mainichi.jp "創世期"
gives 5 hits, all used like 創成期 or 創生期. For example, one is on the establishment of the Rolex watch company.
(創成期 gives >100 actual results, 創生期 13 actual results)

[iK] or [sK], I don't get the vibe that it's a good practice to use 創世期, in spite of the ngram occurrence. A lot of potential confusion with 創成期；創生期 ad 創世・創世記（the creation of the world/the Book of Genesis）.  But then again, perhaps it's not confusion, but deliberate.

Maybe we can't [iK] though... I leave it to you

@@ -8,0 +9,4 @@
+</k_ele>
+<k_ele>
+<keb>創世期</keb>
+<ke_inf>&iK;</ke_inf>

創成期	24689	13.9%
創生期	15270	8.6%
# Possibly a giant mistake...
創世期	6930	3.9%
# Genesis (bible)
創世記	130434	73.6%

https://www.weblio.jp/content/創生期
創生期
読み方：そうせいき
物事が初めて生じた時期。当初。「成立」に焦点を置く場合は「創成期」の表記も用いられる。

This is the example given in weblio, a wikipedia section header identifying the initial stage of adult video games:
https://ja.wikipedia.org/wiki/アダルトゲーム
創生期（1980年代） <-- the 1980s "early period" seems like a fine gloss. 

https://eow.alc.co.jp/search?q=創成期
会社の創成期に
during the company's early days

実用日本語表現辞典 puts 創成期 as a variant of 創生期, with a nuance of "founding".  創成期 wins on ngrams, probably because things get founded more than created randomly.  But 創生期 may actually be more general.

"early days" popped up in eijiro (the only gloss it has, on 創成期).  This formulation also shows up in reverso here-and-there, and seems like a pretty natural equivalent to me.  Also clarifies the nuance of the whole term.

As you might imagine, the glosses for 創生期 are more "creation"-heavy...  These kanji are not completely interchangeable, but I don't  know if we want *4* entries for そうせいき

@@ -5,0 +6,3 @@
+</k_ele>
+<k_ele>
+<keb>創生期</keb>
@@ -13,0 +17,2 @@
+<gloss>early days (e.g. of a company)</gloss>
+<gloss>early years (e.g. of an industry)</gloss>

gg5

プログレッシブ和英中辞典: https://kotobank.jp/jeword/創成
研究社新英和中辞典: ((in)) the early period; ((in)) the initial stage.

gloss different from 創成, so probably worth a new entry