Is the transcription accurate or authoritative?
The text seems from 二祀邲其卣, and transcriptions vary considerably.

http://www.dpm.org.cn/collection/bronze/234458.html?hl=%E4%BA%8C%E7%A5%80%E9%82%B2%E5%85%B6%E5%8D%A3
http://www.gwz.fudan.edu.cn/Web/Show/3040
http://hsyt.voc.com.cn/view.php?tid-3884-cid-156.html

> Withdraw as correct transcription should be U+2C1B5.
Keep pending further evidence.

Keep pending additional evidence.

The evidence is is sufficiently authoritative. There are often several different transcriptions of bronze script characters, and it is not the job of IRG to determine whether a transcription is academically correct or not, only to determine if the transcription is required for encoding or not. The evidence indicates that this character is required for encoding, and as it cannot be treated as an IVS for U+2C1B5, it should be encoded as a separate character. Therefore move back to the M set.