Open-SearchEngine allows for two types of indexes: URL and Directory.

There is no limit on the number of urls or directories that can be indexed by the spider, but yes there is a difference in how the paths are stored.

Since URL paths are stored in a dedicated table, there is no issue in adding urls to one's satisfaction.

One the other hand, Directory paths are stored in teh ScheduledItemSettings table as a string, and there is a limit of 256 characters for the total length of all the combined paths.
This has caused issues, where some of the paths were truncated.

To circumvent this issue, you can apply a simple change to the DB table, that will increase teh space available from 256 characters to 3500.

Just run the following script from your Host/SQL menu in DNN:

Alter table dnn_ScheduleItemSettings
ALTER COLUMN SettingValue nvarchar(3500)

Now you can add directories to index, without worring about them getting truncated that easily.