OK

@@ -22 +21,0 @@
-<s_inf>also written 圕</s_inf>

I don't think we need that note for such an obscure form (on such a common word). I propose dropping 圕 altogether. It's recorded in kanjidic.

It gets 664 Google hits, and after you subtract the pages of kanji lists and the pages derived from Jmdict there are only a few real ones; mostly referring to old texts. I saw "圕研究" a couple of times. I guess an "also written" will do.

@@ -22,0 +22,1 @@
+<s_inf>also written 圕</s_inf>

kanjigen:
【圕】
｛名詞｝図書館。
「囗＋書」の会意文字。「図書館」を一字であらわしたもので、ｔú　ｓｈū　ｇｕǎｎと読む。中国で用いられる。

Confirms the meaning, and to some extent the reading.  Perhaps it should be an "also written as".

You wouldn't find 圕 in those references because their online editions have restricted kanji sets.
The Japanese Wikipedia entry for 図書館 used to begin: "図書館（としょかん、古くに圕とも）とは、...". at some stage the "古くに圕とも" was deleted (I haven't hunted through the edits to find out when or why).
圕 is a JIS212 kanji that was kept on in JIS213. In the JIS dictionary, there is the comment "圕は図書館の合字". We have plenty of entries with odd and obscure kanji included, appropriately flagged, and I think having 圕 as an "oK" was really quite appropriate. It should be in the entry somewhere.