This article explains why only 52 items appear in a drop-down list and shows you how to change the control type to a Look-up list if you need to display more.
Less than 52 items to display
The default setting of the searchable drop-down list control type is that it will only show 52 items, however, if you clear any results from the box you will be able to click into the search field and type in the name of the item you are looking for.
The next 52 items alphanumerically from this search term will then be displayed.
More than 52 items to display
If you have substantially more items than 52, then a Look-up list may be more appropriate. You can follow the steps below in the Admin tool to change the Control Type.
From the Admin Tool, click Menus.
Select the desired menu set.
Navigate, on the left menu, to the area that contains the control type to be changed.
Double-click the form that houses the control.
Click the padlock to unlock the form if it is locked.
Double-click the target Control from the left menu.
Expand the basic details section and select the Control Type Dropdown.
In this instance we will change this to Look-up list.
Click Apply.