ModifiedAvail is a Boolean property that indicates if the last modification date and time value in the ModifiedDate property is available for the collection item. 

ModifiedAvail is updated when the registered ListParserClass for the FTP client is used to examine the content in Data in its' ParseLine method. ModifiedAvail will contain False when the remote file system does not provide last modification date and time values, or when the expected listing format does not contain a recognizable marker for the value. 

Use SizeAvail to determine if file size information is available for the collection item.

ModifiedDate 

SizeAvail 

Data 

TIdFTP.ListParserClass 

TIdFTPListParserBase.ParseLine