Does iTunes still use ITUNNORM tags?

iTunes used to write COMMENT ITUNNORM tags to mp3s to store SoundCheck data, but it hasn't been doing that for a while. I still have a lot of songs with that tag. Can I delete the tag from my mp3s with no effect, or would they all have to be reloaded into iTunes to get properly leveled?

Part of why I'm asking is because I often find that older songs with big SoundCheck adjustments (seen when I look at the Volume setting on the File tab in Song Info) do not play at the proper level, especially while playing from my phone in the car. These days I run all my files through MP3GAIN before loading them, but the older files are dealt with as problems crop up. In an ideal world, I could wipe out useless ITUNNORM tags in bulk with mp3tag, but not if they're still being used somehow.

MP3tag does not use ITUNNORM fields.
Isn't that a question for an Apple itunes forum?
Like here:
https://discussions.apple.com/thread/4577967

Mp3tags sees these as Extended Tags. And many many people here have actual experience with them and may have actual useful info to share.

Still, I would consider all these replies as opinions.
In the end it is down to you how you decide and whether you delete the fields for ITUNNORM and stay with replaygain.
On the topic of replaygain, I would like to add that you should watch out to which tags the program writes this information.
There are numerous threads that state their irritation when a program wrote RG information to APE tags but did not update the other tag fields.
In MP3tag, APE tags have display priority over all other tags. So it might look like the other tag information is lost.
Try to get RG information into ID3V2.3 tags.

Doubling down on "I don't know, but I'll reply anyhow" I see. Sigh.

Replaygain has nothing to do with any of this.

Perhaps I mistook this for the presence of replaygain tags ... Sorry.

As noted above, iTunes does not use the standard Replaygain tags for album or tracks. There are some music converters that will write the iTunes gain info while doing Replay calculations. Note however that iTunes is only able to do one of these, so you would have to choose whether you would prefer Album or Track gain. This is not a function of mp3tag.

To your specific request about maintaining the ITUNNORM data with mp3tag - that is completely up to you. If you are still using iTunes to actually play any music, this information is still relevant. If you only use it as a manager for your iStuff, you can delete the tag field. But I guess based on the minimal data size it has, the question would be "Why bother?" if the normalization is already there?