Time information from GPS receiver: how to tell whether it is fresh or stale?
Most of the GPS modules keep on sending the data in the NMEA format whether they have a GPS fix or not, however, you can parse the GPS data to find whether the data is the latest data received from the GPS or not. If you look at the definition of the NMEA data here, there are a few variables in the data that you can use to find whether the data is the latest data from the GPS or not. 

You can use the "Fix Quality" in GPGGA as well as "Validity/Receiver warning" in GPRMC for your module. The tinyGPS indeed has both of these variables being parsed. 

In the tinyGPS library, if _gps_data_good is true then the data coming from the GPS module is the latest data it received from the GPS satellites. The program uses either the fix or validity to determine this (Refer to the library here and here). 

You should just keep checking this variable to find whether the current data is the latest from the GPS or is it being calculated internally.