General principle is that if there is a rule for how the simplification was performed that stretches across several characters, it did not exist independently prior to 1946. The cases where the character did exist prior to 1946 tend to fall into the following categories:
- One of several competing forms was chosen to be the official form
- An older character (or several) was merged into a less complex existing character
In one case a character was both simplified and split out into a second distinct character to allow for further expression of certain nuances. Lastly, in one case a character was actually reduced to its original historical form after removing a component that had previously been added for phonetic reasons.
The kanji involved are listed below according to their grouping. A space separates the 旧字体 form(s) on the left from their corresponding 新字体 on the right. Unless otherwise listed, all entries are sourced from the Online Kanji Etymology Dictionary.
Standardized on a preferred alternate form
- 艷 艶
- 囘 回
- 懷 懐
- 卷 巻
- 卻 却
- 糺 糾
- 堯 尭
- 羣 群
- 劵 券
- 縣 県
- 恆 恒 (Listed as alternates here, although the dictionary is adamant that 亙亘 are distinct characters by heritage)
- 蠶 蚕
- 穰 穣
- 晉 晋
- 刄 刃
- 插 挿
- 瘦 痩
- 窗 窓
- 聰 聡
- 敕 勅
- 鬪鬭 闘 (further simplified the preferred alternate chosen)
- 貳 弐
- 姙 妊
- 黏 粘
- 霸 覇
- 祕 秘
- 萠 萌
- 襃 褒
- 飜 翻
- 槇 槙
- 萬 万
- 麵 麺
- 餠 餅
- 祐 祐
- 遙 遥
- 畧 略
- 鄰 隣
- 凛 凜
旣 appears to have been an alternate to 既, which was simplified to 既.
There are also several which are not called out as explicit alternates by the dictionary, but which would logically appear to have been, including:
- 壞 壊
- 曉 暁
- 圈 圏
- 權 権
- 壤 壌
- 孃 嬢
- 讓 譲
- 釀 醸
- 搜 捜
- 麥 麦
- 倂 併
- 塀 塀
Originally existed as a separate character
罐 缶
藝 芸
冱 冴
絲 糸
- 絲 シ、いと
- 糸 present meanings were originally those of 絲
牀 床
證 証
- 證 ショウ to make a report; testify; evidence
- 証 ショウ correct, admonish
蹟 跡
- 蹟 セキ、シャク footprints
- 跡 セキ、あと footprint, remains, ruins
卽 即
- 卽 ショク、ソク (redirected to entry on 蝍, which provides these readings)
- 即 ソク
臺 台
擔 担
- 擔 タン、かつ・ぐ、にな・う
- 担 タン Originally meant "to knock or beat down"
膽 胆
- 膽 タン、い、きも
- 胆 タン Originally referred to fat/grease, or to lip gloss made from such
燈 灯
- 燈 トウ、ひ Used to refer to a light held up high, such as a torch
- 灯 トウ、ひ
辨辧瓣辯 弁
- 辨 ベン refers to discriminating or making distinctions
- 辧 Considered by some sources to be a variant form of 辨
- 瓣 ベン has to do with petals, valves
- 辯 ベン fluency, speech, or dialect
- 弁 ベン Online Kanji Etymology Dictionary says it "now serves as a simplified form of distinct characters with the element 辡", which strongly indicates previous existence as a separate character, however it does not detail the nature of such.
辮 (braid) is included as another character that usually gets simplified to 弁 in modern usage.
豐 豊
- 豐 レイ to prepare offerings for a festival (祭事に供え物を盛る器)
- 豊 ホウ bountiful
Credit to Zhen Lin and snailboat for this one. Information for these two characters sourced from Wiktionary
豫 予
- 豫 ヨ
- 予 [uncertain about readings] Character formerly used to mean "I" in classical Japanese
餘 余
- 餘 ヨ、あま・す、あま・り、あま・る
- 余 [uncertain about readings] Character formerly used to mean "I" in classical Japanese
慾 欲
- 慾 ヨク Similar to 欲, but contained shades of lust in its meaning as well
- 欲 ヨク、ほ・しい
亙 亘
- 亙 ヨウ extend across, over
- 亘 セン、コウ、とど・く、めぐ・る、わた・る cross over from one point to another
The Online Kanji Etymology Dictionary is adamant that these two are separate characters, in spite of what other sources may indicate.
Split to form a new character to allow for more nuanced usage
From the Online Kanji Etymology Dictionary:
Originally the same character as 著. When 著 came to refer to literary works, 着, a variant of 著 in popular usage, took over the meanings it presently expresses. As with 著, adhere and meet with are via the "pile" concept behind 者. The many extended meanings include wear, put on and dress (← clothing attached to the body), be seated/take up a position and arrive/reach (a destination) → reach (to); counter (for clothes, or to enumerate the order of finishers in a race ← wear clothing; arrive); cover and pin responsibility on.
Returned to an earlier form
This one started out as 処, and later picked up 虍 as a phonetic marker. 新字体 reduced this back to its original state.