@Anonymous
You might have already figured this out, since your latest post was about a year and half ago, but I was having this issue, so it may help someone else (Autocad 2021 here, but I am pretty sure this applies to a lot of previous versions):
Here is how I make a invisible attribute to feed into another note:

This was important because I was originally simply using a single multiline attribute before, which you can't edit quickly and do multiple at once, which makes adding counts for rebar cumbersome. Doing this and putting a field inside "NOTE" linking to "COUNT" after inserting the block into the drawing and then copy and pasting that block works... IF you make sure to UPDATEFIELD > ALL every time you want the blocks to update. Just be careful not to change the "NOTE" value after getting what you want in there.
As to why I needed multiline attributes: single line attributes do not play well with the MIRROR command (MIRRTEXT system variable set to 0), as any change to the text of a single line attribute will result in the text moving away from the point you want the text to remain at with its mirrored justification. Multiline attributes work like you would expect. I didn't even want the FLIP action (dynamic block function), as that is another grip to contend with and I like my blocks as simple as possible.
Doing this, I can select multiple blocks and change the qty in the properties without going through several clicks for each quantity I want to input.
I just tested this: I made the same block described above, then nested that block into another "safety block" with the fields that I wanted into my blocks.dwg. And used the INSERT command to insert the safety block into another drawing, exploded that block, and the original block then works like intended... which means I don't have to go into the FIELD dialog boxes every time I want to use the block anymore.
For the sake of understanding the procedure set up, let's call the used block, block "A", and the block being nested into, block "B"
As a result all I have to do to is insert block B into the target drawing, then explode that block and then copy block A to all the places I need, then use properties to change that block... multiple of them at once if desired.
I just saved at least 30 minutes per drawing using this approach. Granted, I could import quantities by extracting information from blocks, but there are a lot of times where I prefer being able to use standard autocad commands (polyline mostly) for certain rebar, and sometimes there will be overlaid items accidently, so extraction would be dangerous for me anyways.
Oh and ATTMODE controls how attribute visibility works, and should be set to "1". It is drawing controlled, so make sure your template is set right for that.
Cheers! Good luck!
BTW, work is starting, so I have to get to it, but let me know if you want a video of a step and I will get to it eventually.