How is budget calendar and period determined for only project based budgetary controls?

Summary:

We have budgetary control enabled for Projects only (and not GL). When we baseline the budget for the project, a control budget is automatically created.
Also, budget calendar with period is getting created automatically and getting assigned to control budget. Want to understand how this works?

Content (please ensure you mask any confidential information):

We have budgetary control enabled for Projects only (and not GL). It is absolute at project level and track at top resource level. When we baseline the budget for the project, a control budget is automatically created for project and top resource levels. The control budget for project level is showing Budget Calendar as "S_1711969531835" and From and To Periods as "PRD_01-01". Also observed that this calendar and its period was created automatically with description "Single Period Budgetary Control Calendar". In contrast for top resource track level control budget, it is taking accounting calendar which is not even enabled for