むつかしい is in most of my refs.

@@ -26 +25,0 @@
-<re_inf>&sk;</re_inf>

むずかしい	975326	4.8%
むつかしい	124454	0.6%
むづかしい	10868	0.1%

@@ -25,0 +26 @@
+<re_inf>&sk;</re_inf>

むづかしい	10868

@@ -25,0 +26,4 @@
+</r_ele>
+<r_ele>
+<reb>むづかしい</reb>
+<re_inf>&sk;</re_inf>

Indeed.

Google N-gram Corpus Counts
╭─ーーーー─┬─────╮
│ 六借しい │   0 │
│ 六ヶ敷い │ 261 │
╰─ーーーー─┴─────╯

If nikk is the only ref with these old rare ateji forms, they're probably okay to hide.

@@ -12,2 +12 @@
-<ke_inf>&ateji;</ke_inf>
-<ke_inf>&oK;</ke_inf>
+<ke_inf>&sK;</ke_inf>
@@ -17,2 +16 @@
-<ke_inf>&ateji;</ke_inf>
-<ke_inf>&oK;</ke_inf>
+<ke_inf>&sK;</ke_inf>
@@ -31 +29 @@
-<xref type="ant" seq="1157000">易しい・やさしい</xref>
+<xref type="ant" seq="1157000">易しい</xref>

gg5, prog, meikyo
子細	28,879		
子細に	10,255

GG5 and prog have three senses, like the kokugos.
I think we should have an entry for 子細に.

@@ -19 +18,0 @@
-<pos>&adj-na;</pos>
@@ -21 +19,0 @@
-<gloss>details</gloss>
@@ -23,2 +20,0 @@
-<gloss>significance</gloss>
-<gloss>particulars</gloss>
@@ -27,0 +24,9 @@
+<pos>&adj-na;</pos>
+<gloss>details</gloss>
+<gloss>particulars</gloss>
+<gloss>significance</gloss>
+<gloss>meaning</gloss>
+</sense>
+<sense>
+<pos>&n;</pos>
+<s_inf>with neg. sentence</s_inf>
@@ -29,2 +34,2 @@
-<gloss>obstruction</gloss>
-<gloss>interference</gloss>
+<gloss>inconvenience</gloss>
+<gloss>objection</gloss>

GG5:
1 〈事情〉 circumstances; 〈詳細〉 details; 《文》 particulars
¶子細に in detail; 《文》 minutely
･子細に語る give a detailed [full] account 《of》
･子細に点検する make a close inspection 《of》.

The JEs combine those senses, and think it works well.
They also only have 子細, and the kokugos lead with it so I'd leave it as it is.

@@ -20,6 +19,0 @@
-<gloss>detailed</gloss>
-<gloss>minute</gloss>
-</sense>
-<sense>
-<pos>&n;</pos>
-<pos>&adj-na;</pos>
@@ -26,0 +21 @@
+<gloss>details</gloss>

デジタル大辞泉, 旺文社国語辞典

most of my dictionaries have it as the first definition. 

Also as for 子 vs 仔, I think 仔 is the correct kanji for this word since it has the detailed/minute meaning and is used in the examples:

し【仔】
① こまかに。くわしく。「仔細」
② こ。動物の子。「仔牛（こうし）」

し【×仔】
㊀〈シ〉小さい。細かい。「仔細」
㊁〈こ〉動物の子。「仔羊」

@@ -16,0 +17,6 @@
+<sense>
+<pos>&n;</pos>
+<pos>&adj-na;</pos>
+<gloss>detailed</gloss>
+<gloss>minute</gloss>
+</sense>

Certainly both are sanctioned, although 大辞林 tags 仔細 as deprecated.
I'll go the the 常用漢字 one first, I think.

Meikyo vt and vi additions to n,vs entries
-*- via bulkupd.py -*-

@@ -18,0 +19 @@
+<pos>&vi;</pos>

gg5, prog

I think this is clearer. "Year" makes more sense than "class" for the first gloss.

@@ -19,2 +19,2 @@
-<gloss>repeating the same class (school)</gloss>
-<gloss>staying in the same class for two or more years</gloss>
+<gloss>repeating a year (at school)</gloss>
+<gloss>staying in the same class for another year</gloss>

大辞泉 大辞林

@@ -20,1 +20,1 @@
-<gloss>staying more than two years in the same class</gloss>
+<gloss>staying in the same class for two or more years</gloss>

GG5, correspondence.

@@ -14,0 +14,1 @@
+<gloss>Councillor</gloss>

Entry created

@@ -14,1 +14,1 @@
-<gloss>miniscule</gloss>
+<gloss>minuscule</gloss>

Entry created

Don't need to explain it.

@@ -18 +18 @@
-<gloss>sweet potato shochu (distilled liquor)</gloss>
+<gloss>sweet potato shōchū</gloss>

daijr, 33 ngrams

@@ -8,0 +9,3 @@
+</k_ele>
+<k_ele>
+<keb>薯焼酎</keb>

koj, daij, gg5

@@ -6,0 +6,3 @@
+</k_ele>
+<k_ele>
+<keb>藷焼酎</keb>
@@ -12,1 +15,1 @@
-<gloss>potato shochu (distilled liquor)</gloss>
+<gloss>sweet potato shochu (distilled liquor)</gloss>

Entry created

merged

I agree, and I have drafted a merge, with "usu. ...." to emphasise that さかい is primarily used for "border; boundary".

could be merged into さかい

koj, daij, meikyo, prog, gg5, ddofbud

I guess so.

@@ -13,1 +13,1 @@
-<gloss>Mother (Mother Earth, Mother Nature)</gloss>
+<gloss>Mother (as in Mother Earth, Mother Nature, etc.)</gloss>

英辞郎

Used in a few set phrases, clearer to have a separate naru-adjective entry.

"earth mother" has a different meaning.

@@ -10,0 +11 @@
+<pos>&exp;</pos>
@@ -13 +13,0 @@
-<gloss>earth mother</gloss>

ははなるだいち	82
ははなるたいち	No matches

cf. 大地

@@ -8 +8 @@
-<reb>ははなるたいち</reb>
+<reb>ははなるだいち</reb>

this entry gets the parsing wrong.  all of the entries in eijiro are 熱+[成~]  (i.e., in 熱成形, 熱- is a prefix to 成形; -形 is not a suffix to 熱成).  added 熱成形

英辞郎 lists 18 forms, notably 熱成形 and variants.

Primarily used in various compounds (forming, shaping), sometimes used in isolation or genetive (e.g., for heat-aged 焼酎).

なるほど

eij, looks like 150k hits

see rejected 2648840

@@ -15 +15 @@
-<gloss>Kumamoto rice shochu</gloss>
+<gloss>Kumamoto rice shōchū</gloss>

koj, daij

daijs, gg5

i think the pref sense should go first

@@ -11,8 +11,1 @@
-<pos>&n-suf;</pos>
-<xref type="see" seq="1164500">一駄</xref>
-<gloss>load</gloss>
-<gloss>pack</gloss>
-<gloss>horse load</gloss>
-</sense>
-<sense>
-<pos>&n-pref;</pos>
+<pos>&pref;</pos>
@@ -27,0 +20,8 @@
+<pos>&n-suf;</pos>
+<pos>&ctr;</pos>
+<xref type="see" seq="1164500">一駄</xref>
+<gloss>load</gloss>
+<gloss>pack</gloss>
+<gloss>horse load</gloss>
+</sense>
+<sense>

GG5

@@ -13,2 +13,2 @@
-<gloss>a load</gloss>
-<gloss>a pack</gloss>
+<gloss>load</gloss>
+<gloss>pack</gloss>
@@ -16,0 +16,9 @@
+</sense>
+<sense>
+<pos>&n-pref;</pos>
+<xref type="see" seq="1409070">駄文・1</xref>
+<gloss>poor</gloss>
+<gloss>low-grade</gloss>
+<gloss>trivial</gloss>
+<gloss>insignificant</gloss>
+<gloss>worthless</gloss>

GG5、大辞林、広辞苑

Appears in 狂言「しびり」 in form 五駄や十駄

if it has to be one of the two, certainly.

Eijiro, http://www.if-j.co.jp/yogo/data50/yougo-u.html

I think I refer the noun.

@@ -5,1 +5,1 @@
-<keb>表見返しに</keb>
+<keb>表見返し</keb>
@@ -8,1 +8,1 @@
-<reb>おもてみかえしに</reb>
+<reb>おもてみかえし</reb>
@@ -11,2 +11,4 @@
-<pos>&exp;</pos>
-<gloss>on the inside of the front cover</gloss>
+<pos>&n;</pos>
+<xref type="see" seq="1604410">見返し・みかえし・1</xref>
+<gloss>inside of the front cover (of book)</gloss>
+<gloss>front end-paper</gloss>

『脳みそが筋肉』の略。 indeed.

http://ja.wikipedia.org/wiki/脳筋
http://d.hatena.ne.jp/keyword/Ǿ��
http://www.google.com/search?q="脳筋"