2.2.41 [RFC5545] Section 3.4, iCalendar Object

V0051:

The specification allows multiple iCalendar objects to be sequentially grouped together.

Microsoft Office Outlook 2007, Microsoft Outlook 2010, Microsoft Outlook 2013, Microsoft Outlook 2016, Microsoft Outlook 2019  

On export, Outlook only exports one VCALENDAR component per iCalendar file or MIME part.

On import, Outlook can parse iCalendar files with multiple VCALENDAR components. However, only the properties of the first VCALENDAR component are used.