For this case, it's reliable enough to encode because it a simplified form of a tranditional character. There is no need to provide a reliable evidence of place name.
It may be a stable error. There are different versions of 1958/1964/1966/1971/1980 陕西省公路里程表, I will check some of them. And I suggest we keep it in main set for now.
It is included in 《八辅》
And the article doesn't say 赤崁 is written as 赤⿱宀坎 but 赤嵌. As to this article, the anthor just list all characters used as same meaning and then give statement about all of them .
What's more, it's used in Fujian Province too.
In Andrew's opinion, does 《宋元以来俗字谱》seem reliable enough? I don't think the comment is reasonable. Besides, all other corresponding relationships in the evidence is clear and right.
For example,赣 and 㶥
江西省广昌县地名志，P226-227
According to the evidence, ⿱山畬 and ⿱山𤲞 has the meaning of 斜坡. They are congnate but have the different meaning of 畬.
In place names, 畬、畲 and 𤲞 can be used as each other. But there are not too many pairs.
As I know,
For radical 土, there are 𰊮（U+302AE）, ⿰土畲 and ⿰土𤲞;
For radical 山, there are ⿰山畬、⿰山𤲞、⿱山畬（WS2017）、⿱山𤲞.
However, 𤲞 is also a variant of 番 which means ⿰土𤲞 can be a variant of 墦, ⿰山𤲞 can be a variant of 嶓.
Considering people will more likely to think 余 and ⿱人米 as different characters, I suggest we encode them seperately.
New evidence
http://www.koreanhistory.or.kr/newchar/list_view.jsp?code=70922
I think here is a case that ⿰土𤲞 is a variant of a 墦 (坟)：
The glyph is not very clear. According to the context and the evidences, it is hard to decide whether the vertical stroke should be out of the bottom bar or be out of the upper bar. So I suggest we pending this character for further investigation.
IRG Working Set 2021v3.0
Source: Xieyang WANG
Date: Generated on 2022-11-27
Unification
Evidence
甘肃方言土语集
And the article doesn't say 赤崁 is written as 赤⿱宀坎 but 赤嵌. As to this article, the anthor just list all characters used as same meaning and then give statement about all of them .
What's more, it's used in Fujian Province too.
For example,赣 and 㶥
According to the evidence, ⿱山畬 and ⿱山𤲞 has the meaning of 斜坡. They are congnate but have the different meaning of 畬.
In place names, 畬、畲 and 𤲞 can be used as each other. But there are not too many pairs.
As I know,
For radical 土, there are 𰊮（U+302AE）, ⿰土畲 and ⿰土𤲞;
For radical 山, there are ⿰山畬、⿰山𤲞、⿱山畬（WS2017）、⿱山𤲞.
However, 𤲞 is also a variant of 番 which means ⿰土𤲞 can be a variant of 墦, ⿰山𤲞 can be a variant of 嶓.
Considering people will more likely to think 余 and ⿱人米 as different characters, I suggest we encode them seperately.
I think here is a case that ⿰土𤲞 is a variant of a 墦 (坟)：
The tone could vary in different dialect.
If experts think this to be unclear, I'd like to buy a hard copy and take a picture myself.