Hi Mehfoos L Yacoob,
Greetings. Thank you for posting the thread to our community.
Based on your description, it seems you have concern on the definition of “% Complete” field in Planner Premium task.
After my research and as far as I know, it is indeed that there’s no direct documentation of explaining all fields in Microsoft Planner Premium. However, Planner premium is actually the migration from the Project for the web which is very simple project management tool that designed from Microsoft Project. For your reference: What is Project for the web? - Microsoft Support.
To put it simply, all the fields you can find in Planner premium is actually equal to the same fields in Microsoft Project. In that case, here is the related Official support article as reference for you: Percent (%) Complete fields - Microsoft Support. I suggest you can review this support article to get more definition about the "% Complete" fields in Microsoft Planner.
Meanwhile, Personally, I’m totally agree and understanding the confusion of this scenario causing to you. Having a full detailed documentation of the fields in Planner premium plan is definitely helpful to Planner users to maximum use Microsoft Planner. Due to this situation, I also suggest you can go to this link: Planner · Community (microsoft.com) to go to our Feedback community and send your feedback and requirements. Our product team is in charge of the site, and they constantly check customer reviews and feedback, and all Microsoft product related info are developed and improved based on customer feedback.
Please notice and accept my apologies that as moderators in the community, we are not responsible for the product design and documentation for Microsoft products. To help you send your feedback and requirement to the related development team, we have redirected you to the correct path.
Greatly Appreciate for your patience and understanding.
Hope you having a nice day and really much warm regards to you as well! 😊
Sincerely,
Harry | Microsoft Community Moderator