Implied erhua in writing?
There is such text in the 凡例 section in 《现代汉语词典》：

书面上有时儿化有时不儿化，口语里必须儿化的词，自成条目，如【今儿】、【小孩儿】。书面上一般不儿化，但是口语里一般儿化的，在释义前面加‘（~儿）’，如【米粒】条。……

The text shows how 儿化 is shown in the entries and explanation. The words with 儿化 are mainly divided into two groups: 1. Words that are sometimes written with 儿 and sometimes not, but are always pronounced with 儿化 2. Words that are usually not written with 儿, but are usually pronounced with 儿化.
It shows that there are words that would not be written with 儿化, but would be pronounced with 儿化. Each word has its own tendency as whether it would be written with 儿.
(Note: all 儿 in the quoted text showing 儿化 are in small font in 《现代汉语词典》.)