Index native_stdout.log with no dates but only time-stamps

Trying to index a native_stdout.log that has no dates in the first line and only has time-stamps. 07:26:49,602 INFO [ServerImpl] 07:26:49,602 INFO [ServerImpl] 07:26:49,602 INFO [ServerImpl] 07:26:49,602 INFO [ServerImpl] 07:26:49,602 INFO [ServerImpl] Splunk indexed the file by using the file modified date. Is this the expected behavior when the log file has no dates?