attribute add-update fails to update storefront labels

[Giuliano69]

Describe the bug
In [Usage] (https://docs.m2if.com/37/getting-started/usage) the shortcut add:update seems referred to apply only to product (function description is about product catalogue and sku)
but testing ALSO with attribute:import this kind of add-update seems to be also present in attribute:import
(First issue: maybe ad addendum to the doc may better describe this functionality)

We can APPEND new values in the attribute list, with the corresponding language labels.
BUT seems the add:update CANNOT update the labels for the attribute label in the storefront for other languages.

To Reproduce
I enclose the two examples I made to add-update the basic attribute "manufacturer" (that is part of the basic Magento2 install), in two steps.

1. The firs csv appended new attribute values in requested languages, AND updated the storefront label for said languages. (from Manufacturer to Brand , for all languages)
2. The second csv appended the new attribute value (e.g. Pelikan) but FAILED to update the Italian manufacturer storefront label from "Brand" to "Marchio"

bin/import-cli-simple.phar import:attributes add-update

https://drive.google.com/file/d/1Doh8olGvHMt3xEfpQkyeHDCXyB1b_Sfm/view?usp=sharing
https://drive.google.com/file/d/1jOn-oBv-Ej1AIsm9vMPpaKUsHrlonO5-/view?usp=sharing

Expected behavior
The italian label for manufacturer should change to "Marchio" after the second attribute:import

Screenshots
https://drive.google.com/file/d/14nVno9h1BUVDnto1Rs5RoTBCf3tZh3b3/view?usp=sharing

Desktop (please complete the following information):

• OS: ubuntu 18.04
• Browser [e.g. chrome, safari]
• Magento 2.3.5p1
  -M2IF 3.8.16