"うえがわ" inteded to be "上側" should be a new word or a correction for "うわがわ" ("うわかわ")?

[tats-u]

#1069 (comment)

Mozc or Google Japanese Input can't convert or correct "うえがわ" as "上側" unlike MS-IME & ATOK.

IME	うわがわ	うえがわ	うわかわ	うえかわ
Mozc	✅️	-	-	-
Google Japanese Input	✅️	-	✅️	-
ATOK	✅️	✅️	-	-
MS-IME	✅️	✅️	-	-

Japanese Dictionaries:

Name	うわがわ	うわかわ	うえがわ
広辞苑	Alternative	✅️	-
デジタル大辞泉	-	✅️	-
明鏡国語辞典	✅️	-	-
日本国語大辞典	Alternative	✅️	-
岩波国語辞典	✅️	-	-

"うえがわ" is not registered in any dictionaries, but registered in both MS-IME & ATOK. What is surprising is that ATOK doesn't treat "うえがわ" as a wrong word like "ふいんき".