Month view doesn’t show all my appointments

For this issue, it all depends on how much vertical screen space is available.

When there are more appointments than there is place to show them, you'll get the grey arrow to indicate that there are more appointments for that day.

Some months may show more items per day than others. This depends on how many weeks that specific month spans.

Optimize vertical screen real estate

Short from getting yourself a higher resolution monitor, you can try the following methods to optimize your vertical screen real estate:

• Maximize the Outlook window state
• Minimize the Ribbon
• Disable the Daily Task List

Calendar configuration changes

Aside from optimizing your vertical screen real estate, you can consider the following Calendar configuration changes as well:

• Switch to the week view.
• Decrease the Calendar font
  Right click on an empty space in your Calendar and choose “View Settings…” or “Customize Current View…”. Then click on the Other Settings… button to set a smaller or more compact font.

Select fewer weeks for the Month view

Yet another option would be to select fewer weeks in the Month view.

You can do this by clicking and holding down your mouse button an a day in the Date Navigator (small calendar on the side). Then drag your mouse over the days which you want to select. When your selection spans more than a week, you’re selected weeks will be shown in the Month view.

Another quick way to do this is by holding the CTRL button and clicking in front of the week (or on the week numbers if you have that enabled) to quickly select or deselect a specific week.

Sadly, this change isn’t persistent and you’ll have to repeat your selection when you move away from and then go back to the Calendar folder again.